All right, all right, I'll do this mainly because I don't want to see people doing dumb things like making a Trainer character, hoping to be the best Blue Archmage that ever casted a Thousand Needles. What is this illegible scrawl, you ask? It's just Tyran's class by class evaluation. It's by no means a gospel, but take it from me, newbies often need the help. Oh yeah, and when I say "levelling the class" I mean the class levels, not the class bonuses. You should be using the statbonus command for stats. Also, I'm reviewing the classes for when their tiers are bounded, that is to say, I'm saying what Fighter is like from 1-35, not at 99, for example.
And, screw it, I'm going to just say what each skill does, if it's useful at all, just to stop all the newbies pestering me about stuff they could just as easily look up.
Adventurer
Get the hell out of this class, it has no skills and can only use daggers for weapons. I shouldn't have to explain why that's not a good thing.
Fighter
This is your basic melee class, which branches into the three main fighter-types you'll usually see. It's a good starting point for most, and levelling the class improves its only skill, Tackle, slightly. Stick with swords, obviously. Shield are a bonus to your defense as well.
Skills:
Tackle - Tackle is a short charge time skill that has a chance of paralyzing the mob it's used on. It does decent damage and the paralysis' length is based on class level.
Two Hands - Holds your weapon in two hands (syntax is "twohands [weapon]" instead of "wield [weapon]") to increase damage done by melee and some skills. Can only be used by Fighter classes. In addition, weapons may exist that do not require this skill to be wielded in two hands, and which also aren't limited by the class list above for class restriction. Knightswords are automatically wielded twohanded.
Black Belt
The Black Belt is, well, it's nothing at all until 25. Levelling it as you may or may not notice improves the amount of HP restored by the Chakra command, which is very useful for people of all levels (some levels more useful than others). Chakra is also notable for the fact that it restores SP as well, making it a good support for mage jobs.
Skills:
Spin Fist - This is an attack with roughly the same charge as Tackle, that hits all mobs you're currently fighting. It's not too useful because fighting multiple mobs at once isn't necessarily efficient.
Chakra - Restores HP and SP to yourself. The amount increased raises based on your class level. Having the classes Monk and Sensei also improve the amount recovered.
Thief
Backstab is amazing if you can get a good, strong dagger. You can Steal some nice items (make sure to Assess first to see if the mob has stealable items though) and even make use of Sneak to get past aggressive mobs. Be careful though, as you can only use boomerangs and daggers, neither of which are strong weapon types.
Skills:
Steal - Attempts to steal an item from the mob you're fighting. This works like in FF6, where the item doesn't show up in the mob's inventory. Not all mobs have items you can steal.
Backstab - Opens the fight with a potent burst of damage. Can only be performed with short pointed weapons—daggers, claws, swords, katanas, etc. If you stop the fight somehow, you cannot Backstab again.
Assess - Tells you if the mob has anything you can steal.
Peek - This is the Look command but it doesn't echo "[name] looks at [person/object]" to the room, nothing more.
Purse - Tells you how much gil someone is carrying. This is almost an entirely pointless skill.
Sneak - Hides the "[name] enters/exits" messages, which prevents most aggressive mobs from attacking you, as well as from players seeing you come and go.
Appraise - This works like the Value command in shops, except it tells you how much the price to buy back the item would be.
Hide - Removes your short description (e.g. "Joe the human thief [perfect]") from the room description, making it look like you aren't there. People can still look at you and attack you, however.
Black Mage
Black Mage is phenominal. It's the best class for dealing damage at lower levels, and can utilize most of the elements in the mud (except for holy, obviously). It can't heal outside of Drain, and Osmose isn't much to cry about. It gets Power, which raises your magic power, and a few enfeebling spells. If you're a mage, go get this class.
Spells:
Fire/Bolt/Ice/Stone/Black - Basic elemental spells that deal reasonable damage. They become very deadly if you use the element a mob is weak to.
Light - Creates a light ball that works like a torch. These balls have a duration of one hour.
Poison - This is a mostly pointless status effect that slowly damages its target. The damage actually dealt is very small and the duration between poison ticks is fairly long, plus it only ticks for mobs in combat. It's only really useful on mobs with very high HP.
Drain - Drains HP from the target. Don't do it if the target is undead. Less accurate than you might like, but still a worthy spell at later levels. Wholly worthless at low levels.
Osmose - Drains SP from the target. This is very efficient for keeping your SP up when you can land it consistently.
Precision - Increases magic accuracy. Not much good or bad to say about it.
White Mage
The White Mage is, obviously, the complement to the Black Mage. Its excruciatingly low damage output is matched by its defensive buffs and adeptness at healing. This improves later, as it gains access to more powerful spells.
Spells:
Cure - Cures your target for an amount roughly equal to the spells of the Black Mage, but based on Willpower instead of Wisdom.
Light - See above.
Antidote - Cures poison. Effective if you're fighting Asps.
Safe - Noticeably lowers physical damage you take. This is percentage-based, so it never loses effectiveness.
Shell - See above, but for magical damage.
Image - Raises your target's evasion.
Ruse - Raises your target's magical evasion.
Strong - Raises your melee damage. Not very useful on a White Mage but good if you're subbing it to a fighter class, or are in a group.
Target - Raises your target's physical accuracy. Good to use on party members wielding inaccurate weapons like axes.
Peep - Shows you the HP, SP, base experience, and elements of the target. Very handy to use.
Red Mage
Now this is a starting class. It has access to swords, which as you may have noticed come in the most variety and most damage, as well as attacking and healing magic. It starts off very powerful, but doesn't stay that way at all levels, especially when BLMs become able to outdamage it and WHMs can outheal it.
Spells:
Cure - See above.
Light - See above.
Fire/Ice/Bolt - See above.
Poison - See above.
Safe/Shell - See above.
Strong - Raises your target's physical attack power. This is never useless.
Power - Raises your target's magical attack power. This is never useless.
Time Mage
Time Mage is an odd class to start with. It doesn't get any healing spells aside from Regen, and its offensive capabilities are less than even Red Mage's. However, it can do something no other class can do: manipulate something's charges. Furthermore, it gets the very powerful enfeeble, Mute, entire tiers before Red Archmage gets it. As a party support class, it's not half bad.
Spells:
Eddy - Eddy essentially lowers something's charge, as if they'd not been charging a move at all for some time. In other words, it makes something take longer to resolve a spell or ability. Useful if you can time it right.
Light - See above.
Old - Old is a minor enfeeble to something's "physical" statistics. Not bad, but not great either.
Pause - Pause "resets" something's charge. In other words, if they're trying to use a spell or ability, it makes it as if they'd just initiated it again. This has a very long charge time, however.
Crush - This is simple first-tier nonelemental damage.
Slow - Noticeable battle speed reduction to a target.
Void - This clears the charge of everything in the room, cancelling their currently charging spells and abilities.
Mute - Makes it impossible for a target to cast magic. At low levels, almost no mage mobs are immune to this, making it extremely potent.
Regen - While regen doesn't tick for very much and is pretty slow, this is better than nothing, and is the only healing the Time Mage tree gets inherently.
Jolt - This is the physical opposite of Eddy, raising your target's charge by a set amount. It's a very useful spell if used right.
Caller
Ever since I've remade summoning from the ground up, Caller's gotten a hell of a lot more decent than it used to be. The summons are their own mobs, so they're a lot stronger than just casting a spell and leaving it. Note that while Astral Flowing is very powerful, it's hard on SP. Likewise, it's slower than some other forms of attacking, especially to a solo target. Low Wisdom and Willpower (you need both stats) also makes for weak summons. Caller is, however, spectacular against multiple mobs at once.
Spells:
Chocobo - Summons a Chocobo to fight by your side. The Chocobo has low HP, but high speed and decent attack power. It will spam Tackle and, eventually, Dash.
Ifrit - Summons Ifrit to fight by your side. Ifrit is a pure attack summon, and learns no support moves. However, he hits hard. All of his non-spell attacks have a chance of a critical hit for very high damage.
Shiva - Summons Shiva to fight by your side. Shiva is mainly a mage summon, and learns few non-magical attacks. Her magical attack power is higher than her two counterparts'.
Ramuh - Summons Ramuh to fight by your side. Ramuh is a mixed offensive mage and support summon, being able to not only enfeeble and sometimes even paralyze a mob, but also give you status effects as well.
Entertainer
Mainly a gimmick class. Have fun with Street Talk for kicks, and if you can save your life regularly with Entertain, go wild. Whips are few and far between, so you're again probably stuck with daggers.
Skills:
Entertain - Tries to stop the fight between you and a target. Success is based on Charisma.
Street Talk - Tries to set up two mobs to fight each other. Again, it's Charisma-based. It's a fun novelty skill.
Engineer
Get it for Identify, and Repair if you can find things to repair. Leave it there until later on.
Skills:
Identify - Shows you the stats of a piece of equipment. This is a very, very good skill to have. Getting Mechanic allows you to see how strong an element on something is (e.g. "fire of 10"). Getting Inventor allows you to see how much stats are raised by (e.g. "power_up of 10" instead of simply "power_up").
Repair - Attempts to repair a broken item. Chance of success affected by class level. If you can actually find items to repair, go hog wild or something. This also repairs things broken by the Knight break skills.
Trainer
This isn't a very powerful class at first glance, but it does get a variety of weapon types you can kill things with. None of them are very good though. However, the Camp skill is one of the main features of the Trainer. You can only use it outside of combat, but you heal yourself to full just like at an inn, with the only catch being it doesn't restore SP. Study is like a weakened Peep spell, telling you the mob's HP, SP, and elemental strengths/weaknesses.
Skills:
Study - Shows you the mob's HP, SP, and weaknesses. Good for letting you know what to use on a mob, there's no reason not to have it.
Camp - Sets up camp, which fully restores your HP (but not SP) when it resolves. Extremely handy at any level to have.
Capture - Attempts to capture a mob to be released later. Low success rate based on target's HP and your level.
On to the second-tier classes.