They are both good heros, but I think the kotg is a superior first hero. Mainly, because his ultimate is ALOT better than the naga's. They both can punish a retreating enemy, I think the main difference is that the kotg has great anti-unit spells, while the naga is more of a hero killer. As second hero either is good, they pop out with a great first skill ready to go, really depends on prefrence there. I go kotg 2nd with warden first, and naga 2nd with dh first. I almost never use either of them first, I prefer agi or strength heros first with the exception of the farseer. Both the naga and kotg are 2 of the most mana-hungry heros around, I always seem to need more mana than I have, even with mana pots/wells