Let's see.... Gen 1 is tough, I like them all but my order is probably Venusaur (Tank!)>Charizard>Blastoise.
Gen 2 is Feraligatr no contest, Typhlosion is cool but the Gator is Greater!
Gen 3, Blaziken gets my vote but it is a very narrow edge over Swampert who I've probably used more often on...