Blue: Bulbasaur
Silver: Totodile
Ruby: Mudkip
Leaf Green: Charmander
Platinum: Turtwig
Heart Gold: Chikorita
White: Oshawott
White 2: Tepig
X: Froakie + Charmander
AS: Mudkip
OR: Torchic (I run nuzlockes on this game, so the starter changes; but this was the first one I did)
As for favorites from each gen, since I've restarted a few games often enough to have more than one...
Bulbasaur
Cyndaquil/Chikorita (I really love both of them, can't decide. Totodile's a cutie, too, though!)
Treecko
Piplup
Snivy
Chespin
I've restarted too many times to know which I picked first, and I always alternate for the first 3 restarts so I can trade each to a spare copy (so I have one of each).
I would guess I pick the water one first in each version though. I find them the most appealing for like 5/6 of the games.
Honestly though, I usually just shove it in the PC as soon as I catch my own Pokemon since I don't find the starters that appealing at all. I usually go for the first available flying type I can catch, which is regularly Pidgey. I sometimes trade myself a Pidgey egg and walk around till it hatches in games where Pidgey isn't near the start/not in the game so that I can technically still start with a Pidgey.
Emerald: Treecko
Diamond: Turtwig (Would've done Piplup but the game was used and I didn't feel like restarting. )
White: Oshawatt
Black 2: Snivy
X: Chespin, Bulbasaur
Alpha Sapphire: I think it was Treecko again? I did a semi-egglocke, so I never used whoever I chose.
Gen 1 ~ Charmander
Gen 2 ~ Cyndaquil
Gen 3 ~ Mudkip and Torchic
Gen 4 ~ I don't remember (I know I played it and beat it or most of it).
Gen 5 ~ Piplup
Gen 6 ~ Froakie