Aislinn:Aislinn is a powerful hero to start any map with. Her Meteor Shower is able to clear creatures from before mines and to open passage to new map areas. In larger maps you should consider replacing her by a hero with a better specialty to be your main striking hero.
Charna:Though her specialty is not really useful in other than small maps, Charna still is an above average Necropolis hero.
Clavius:Like many other Necropolis heroes, Clavius has some very potent characteristics (in his case his secondary skills) but one thing that stands in the way of a main striking hero carrier. (in his case his specilty) In small maps Clavius can very well be a main striking hero, in other maps he is quite a good supporting hero.
Galthran:Galtran is an above average Necropolis hero, with powerful secondary skills, but a rather weak specialty.
Isra:Isra is a formidable Necropolis hero, certainly when you want to gather legions of Skeletons.
Moander:In small maps Moander is perhaps the best Necropolis hero, but his Learning loses lots of its power in larger maps where he is but an average Necropolis hero.
Nagash:Nagash has some great secondary skills and he could be a good commander of your armies in a small map. In larger maps he is but an average Necropolis hero, nevertheless he always is a good supporting hero.
Nimbus:Nimbus is the very worst Necropolis hero and above that one of the worst heroes in the game.
Sandro:Sandro is one of the better Necropolis heroes because his spells deal large amounts of damage. He is also one of the most powerful offensive spellcasters in the game.
Septienna:Septienna is one of the weakest Necropolis heroes.
Straker:Straker is one of the worst Necropolis heroes there are.
Tamika:Tamika is one of the best Necropolis heroes and maybe even the best of all. Especially in larger maps and at higher levels, her specialty makes her truly mighty.
Thant:Thant's secondary skills are not that amazing and would even make him a slightly below average Necropolis hero. His specialty however makes him one of the most feared Necropolis heroes in the game. In large maps you could choose to replace him with a hero with better secondary skills, because of the weak Mysticism.
Vidomina:Like Isra, Vidomina is able to raise legions of Skeletons what makes her one of the best Necropolis heroes.
Vokial:Vokial is a great hero in small maps, his Artillery however makes him a lot weaker in larger maps where he could be a garrison hero.
Xsi:Xsi is a below average Necropolis hero, perhaps useful in small maps.