Adela:Adela's Basic Diplomacy makes her one of the best Castle heroes there are, the specialty Bless is not that great but is very useful during the early game.
Adelaide:Certainly not a bad Castle hero, Adelaide's specialty is quite useless what makes her an average quality hero for the Castle.
Caitlin:Caithlin has the formidable advantage of Intelligence, her specialty being 350 gold/day makes her a possible supporting hero (always recruit her unless you've reached the 8 hero limit) or a main striking hero. (in large maps you could consider taking a hero with a better specialty)
Christian:Christian is one of the best garrison heroes you can get, with Artillery and Leadership he will hold off enemy armies longer than any other Castle hero.
Cuthbert:Cuthbert is a below average Cleric. The Estates skill could make him a supporting hero though.
Edric:Edric is an average Castle hero, but not good if you need a powerful spellcasting hero.
Ingham:Ingham is an average Castle hero, thus not worth being a main striking hero.
Loynis:In small maps, (maybe medium) Loynis has a true advantage with his Learning. The Prayer specialty is also not to be underestimated. Do take the Water Magic secondary skill if you can with Loynis, mass Prayer is really super.
Orrin:Orrin is quite a good Knight, but as with all other Knights not good at casting spells. Very nice main striking hero if you plan to create an army of ranged attackers, but only in medium to large maps. (useful for Tower creatures as well)
Rion:Rion's First Aid skill and tent could possibly make him an acceptable garrison hero, but he's not worth more than that.
Sanya:Her Eagle Eye makes her the worst Cleric and one of the worst heroes in the game.
Sir Mullich:Sir Mullich's specialty is both unique and quite insane. This is without doubt the best overall Castle hero and one of the best in the game. Unfortunately it isn't but after level 10 that he can start some decent spellcasting.
Sorsha:In small maps you can focus on the power of Crusaders, giving them some extra power makes Sorsha quite a good Castle hero in smaller maps.
Sylvia:The Navigation Knight, only useful for that purpose. If you're in a map with water, get Sylvia on a boat as soon as possible.
Tyris:Tyris is an above average Knight, her Tactics allow Champions to attack on the first combat turn!
Valeska:In small maps the power of Marksmen can be increased by Valeska, in every other situation Valeska is but average.