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 playthroughs. Sceptile is cool but just overshadowed by Mudkip/Torchic imo.
Gen 4 is Infernape, I have mega nostalgia for him and he just beats up on EVERYTHING with that STAB combination!
Gen 5 is, uh, Samurott? Kind of a forgettable round for me.
Gen 6 is Greninja, as one of the cooler pokemon they've ever made imo.
Gen 7 was cutie grass Owlet all the way, only reinforced by Decidueye the ghost archer!
Gen 8 I'm hardcore Grookie Gang, and I stand by it - although this gen is all too humanlike for my tastes, at least Rillaboom is based off an animal that has humanlike characteristics. But the giant man-hands chameleon and "regular dude with a rabbit mascot head" just are NOT my taste at all.