Bulbasaur- 80% of the time
Squirtle- 20% of the time
Chikorita- 90% of the time
Cyndiquill- 10% of the time
Treeko- 90% of the time
Torchic- 10% of the time
Turtwig- 60% of the time
Piplup- 40% of the time
Snivy- 50% of the time
Tepig- 25% of the time
Oshawott- 25% of the time
I feel all the Kanto starters are great and all equal in terms of overall usefulness throughout the game. Squirtle holds the slight edge, because it was my first.
Just my opinion. Totodile is balanced and crunch helps with Morty's gym.
Mudkip 25 %
It would be an even 50-50 if we were talking Ruby and Sapphire, but because of Emerald and wallace as champ, Treecko becomes very useful in emerald.
The 10% is all based on design. Not a great generation of starters. I would prefer not to use any of them really.
Another just ok generation of starters. Serperior is the best looking starter evolution ever, but a terrible pokemon. Oshawott line is awesome, but the Tepig line is a huge fail for GF, IMO.
I replay games like a madman so no way I'm going to even attempt percentages?
I'm just going to go by my favorites with each.
Kanto - Squirtle, occasionally Bulbasaur
Johto - Chikorita. No exceptions.
Hoenn - All of them because they all rock.
Sinnoh - Piplup. No exceptions.
Unova - All of them because they all kinda suck so meh.
Some of the games I've only played once, so that's why my percentage is at 100% (even though I might choose a different starter the second time around).
Bulbasaur 33%, Charmander 67%, Squirtle 0%
Growing up, it felt wrong not to take Charmander and have it evolve into an awesome Charizard. One of the more recent times I played, though, I started with Bulbasaur, but I found I didn't enjoy my playthrough quite as much. And I've always liked Squirtle, so I'm not sure why I've never used it.
Chikorita 33%, Cyndaquil 33%, Totodile 33%
Of the 3 main runs I can remember playing in Johto-based games, I had no particular preference towards my starter Pokemon. All 3 of them stayed on my team for the majority of the game, but they all ended up taking a back seat to my other Pokemon.
Treecko 50%, Torchic 0%, Mudkip 50%
While these numbers looked like I favored Treecko and Mudkip equally, my Sceptile ended up being my best Pokemon in Sapphire, and I still have my original one from 9 years ago on my current HeartGold.
Turtwig 0%, Chimchar 0%, Piplup 100%
One of the regions where the numbers are stacked in favor of one Pokemon due to only one playthrough. However, my Empoleon became a powerhouse on my team, and I really liked the Water/Steel typing, so I would probably choose Piplup again if I ever went back for another run.
Snivy 0%, Tepig 0%, Oshawott 100%
And the other region with a skewed number. My Oshawott -> Samurott didn't play as big of a role on my team as I was expecting, but it held it's own. When I get B/W2, I'm leaning towards choosing Tepig as my starter, but I'm not fully decided yet.
Kanto - Squirtle (I loved its anime personality)
Johto - Cyndaquil (It's cute, and most useful starter in G/S/C/HG/SS)
Hoenn - Mudkip (Yes, I really do liek Mudkipz)
Sinnoh - Chimchar (Because I love monkeys)
Unova - Oshawott (You all know why I love him, he's super adorable!)
As you can tell, I usually favor Fire and Water starters. Some Grass starters are okay in terms of design but I don't work well with Grass.
I give grass starters their love, since I do also really like Chikorita and Treecko. But as you can see it's mainly Water and Grass starters for me. Everyone else can keep their fire types hahaha. Not saying I hate 'em, but I just like another starter more.