Anyone remember when Schneeente did one of these? no? Well, there's been a few changes since, but I don't think my top 3 is too impacted.
I'm an elf player, but I think I can speak a bit on dwarves behalves too.
Top 3 elf:
Vortex - clear top 1. You unlock her, and you start smashing goblins left and right while your dwarven friends look to you with jealousy. If skilled and used properly she can also work lategame as an infantry punching bag.
Nacris - One would think Cerulean or Mollus takes the cavalry trophy, but no, Nacris does. Pumping up Nacris makes her a great anti-algus/apache/coron killer and she still holds her own against dwarves like Darrak.
Talindra / Vyshaan (the one with the 25% attack bonus, her name's supposed to be Vyshaan I believe, but ingame it's Talindra :shrugs:) - I didn't expect much of this new warlord, but even on Island 4 she destroys goblin towers alone, and she's great when you have too much inf.
Top 3 dwarf:
Darrak - No contest the greatest warlord in the game. There's a joke that goes: How to counter Darrak? You fight him with an even stronger Darrak.
Marduk - Get's my 2nd spot for being one of the few cav dwarf warlords, and also for being one of the most annoying warlords in the game,
Daerkurr - Massed Breathing Bastion on this guy packs a punch!