The eternal question: which heroes are better, mages or warriors?

I think the best hero is the one with well-developed magic skills, specifically air, water, earth, and fire magic, and maybe some other bonuses for magic. This is for HoMM3. As for HoMM5, it would be light, darkness, chaos, summoning, enchantment, or spellcraft magic. Oh, I forgot to mention that all of this should be at the EXPERT level and fully researched (for HoMM5).