Which Hero from Heroes of Might and Magic III is the best?

You can create a lot more snipers from archers than you can from wizards in a Tower.

I'll defend the Dragon one more time: don't forget that he can turn both wizards and monks into Wizards - so on maps where there is both a Tower and a Castle, the Dragon's archer army can grow faster than Jelu's or other heroes'! Finally, even one Wizard, especially at the beginning of the game, provides invaluable help in battles with his expert magic alone! This is often more important than the damage dealt by Wizards, which you are comparing here! Besides, unlike master djinns or fairy dragons, Wizards never cast anything undesirable - and this is not uncommon for the latter!
P.S. Oh, no, I take back my last words about Wizards: now they have cast Air Shield during the siege of the castle - I'll have to start the battle again! :( That is, it would be good if it weren't for the "ancient" bug in "Heroes" that increases the damage from towers instead of reducing it.