First time ever playing Pokemon, I started off with a Squirtle. I'm assuming that you might be talking about starters in general, though, so here's what I chose first time I played each respective game:
Blue- Squirtle
Crystal- Chickorita
Ruby- Mudkip
Emerald- Torchic
FireRed- Bulbasaur
Diamond- Turtwig
Platinum- Chimchar (though I boxed it so I could try using Ponyta)
SoulSilver- Cyndaquil
HeartGold- Totodile
Black- Snivy (boxed later)
White 2- Oshawott
Y- Greninja
OmegaRuby- Mudkip
Diamond: Chimchar Black: Snivy White 2: Snivy, then Oshawott Y: Chespin Alpha Sapphire(I don't have it, but when I get it I am getting mudkip NO MATTER WHAT): Mudkip
Blue - Squirtle
Silver - Totodile / 2nd playthrough with Chikorita
Pearl - Piplup
Soul Silver - Chikorita
Heart Gold - Chikorita lol
White - Oshawott
Black 2 - Snivy
X- Chespin + Squirtle
Alpha Sapphire - Treecko
I did play an emulated version of Sapphire once and picked Torchic, but probs can't count it..tho Torchic ftw my fave fire starter. But yeah, I'm definitely more a Water and Grass kind of guy.
Torchic! It's my favourite Hoenn starter and I picked Torchic in the original Sapphire Pokemon game so I just HAD to choose Torchic again. Ironically, despite how great Blaziken is, Gardevoir ended up being by go to Pokemon on my in game team. xP
(I'll only list off the games I did play more often then the rest)
Gen 1: I didn't play this one fully yet
Gen 2: Neither this one
Gen 3:
Ruby - Torchic
Sapphire - Mudkip (I think)
Emerald - Treecko
Fire Red - Bulbasaur
Gen 4:
Pearl - Turtwig
Platinum - Chimchar (I think)
HeartGold - Totodile
Gen 5:
Black - Tepig (I think)
White - Oshawott
Black 2 - Oshawott
White 2 - Oshawott
(I sorta had an Oshawott fetish)
Gen 6:
X - Froakie
Y- Fennekin (Was going for Chespin, but instead the day before it released worldwide I said "Nah, F it" and went with Fennekin)
Alpha Sapphire - Mudkip (Because bruh, also I didn't want a starter in my adventure party)