Yeah, it is one of the hardest decisions to make on Pokémon games! Hopefully my tips can help you decide which one to pick! ^_^
So stat wise, Bulbasaur. It has a total of
318. Squirtle is 4 points lower, coming at
314. You probably didn't expect this, but Charmander is the lowest, with
309 as a base stat total. But this doesn't mean it's the worse. It'll definitely get better and still has some pros about it, which I'll say about in a little.
Bulbasaur is the
Seed Pokémon. Here are it's stats:
HP : 45
Attack : 49
Defence : 49
Sp. Atk : 65
Sp. Def : 65
Speed : 45
As you can see, it's major stats are
Sp.Atk and
Sp.Def. That means it's better to be used as a special Pokémon. The unfortunate thing is that by level-up, it doesn't learn any Special moves. According to my sources, all it learns are status and physical moves. Even Razor Leaf is physical. Although you could get something outta TMs, but I haven't totally looked into it. I'm pretty sure it should be able to learn some special TMs, at least as a Venusaur.
You might of have heard from Prof. Oak's description while viewing Bulbasaur in FireRed/LeafGreen. It has a Medium-Slow level up rate, which is exactly the same for the other starters, so what Oak says is not exactly true. But it's a good Pokémon as it can pack a punch and hold out, especially in the special area.
When it evolves to
Ivysaur at
Level 16, it can learn its first special move by level-up at Level 44; Solar Beam. Such a shame it's not got much, haha. It's Attack boosts up to 62 while the Defence goes to 63, while the Sp.Atk/Def reach a high amount of 80. Especially for a Pokémon who's not a final evolution.
It definitely gets amazing when it evolves to
Venusaur, at
Level 32. Keep in mind that it evolves the earliest out of the three, so that is a pro. It gets that Atk/Def boost to 80, and it's special stats go all the way up to 100; now it can really tank a lot of things and be real powerful. The only real con is that a fast Fire-Type could really outmatch Venusaur, although it does have good Defences.
Now we go to
Charmander! ^_^
HP : 39
Attack : 52
Defence : 43
Sp. Atk : 60
Sp. Def : 50
Speed : 65
First thing I'm going to say here is about it's
Sp. Atk and
Speed stats. Similar to Bulbasaur, but instead of the Defence, he's all about that Speed. Very fast for a first stage Pokémon, especially that early in the game. And unlike Bulbasaur, a LOT of its moves are special. It's movepool is very diversed, including a variety of Physical, Special and Status moves. A pretty cool choice, to be honest. And it's design is really cool! It has a flame coming out of his back.
Charmander can also learn a good amount of TMs, including good ones. It can even learn a Dragon-Type move, despite being so small and just a plain Fire-Type. It learns it's first Fire-Type move
Ember at Level 7 (which is also special ^_^) and this can be a real help throughout the game, from sweeping in Viridian Forest to beating Erika in Celadon in one try. Especially with that added Flying-Type it gets on its final evolution! It's also resistant to 5 types, these are:
Bug, Steel, Fire, Grass, and
Ice. (Not counting Fairy as that isn't even in Gen III) Not bad! But then again it's weak to 9 types! Just a plain Fire-Type's enemy, I guess. But it all makes up for it when it evolves ^_^
It evolves into
Charmeleon at the regular level, which is Level
16. It's main stats (Sp.Atk and Speed) are increased to a good 80. It's attack is also at a 64! It becomes a pretty viable Pokémon at this stage, but still isn't a dual type. Good thing it gains one when it reaches it's final evolution! Charmeleon's base stat is 405. Good for a Pokémon of its stage!
Then, it evolves into it's final evolution,
Charizard at Level
36 like Squirtle. It is really overrated, but for a reason! A LOT of people like it for it's design. It's just too awesome. Also mentioning that it looks like a dragon (such a shame it isn't). But yeah, it's a Fire/Flying Type, which is really good against Grass-Type. Then its got that horrendous Rock-Type weakness. It can easily get knocked out by a simple Rock Throw, so make sure to watch for that.
It has a base stat total of
534, and it's Special Attack, rises higher then it's usual Speed, and hits a 109 stat. But the Speed hasn't given up! It's still at a good 100, so it's a special fast hitting Pokémon. Very useful in the right situations, but bad in the wrong situations. ^0^; Now it's time for the last one,
Squirtle! o3o~
HP : 44
Attack: 48
Defence: 65
Sp. Atk: 50
Sp. Def: 64
Speed: 43
It's good a pretty decent base stat pool. It's main stats are
Defence and
Sp. Def. It's physical is slightly higher then it's special, although that doesn't make much diference. Very good against Pokémon, as it won't faint as easily as the others, thanks to its shell! Yay for Squirtle! It's good against Brock, Blaine and Giovanni (I'm probably missing one) but that's 3 Gym's you know for sure you won't keep having to go over and over. Personally, Squirtle is my favourite because it's final evolution Blastoise is just... so amazing! I can't really say much, haha. But it's all up to you.
It evolves into
Wartortle at Level
16. It's skin tone turns into a more stronger blue, and it grows a tail and horns or whatever they are that are a white with a touch of a small blue. Just like all of the other starters when they evolve, it gets a boost in pretty much every stat, but a lot in it's 2 mains, being
Defence and
Special Defence. They go to
80, and the Attack and Sp.Atk go to
63-65. You'd obviously expect more for the special if you've used it before, but that proves how bulky it can be. It can tank out a lot of weaknesses if they aren't obvious, unlike Fire. But it's got 4 weaknesses, which are:
Steel, Fire, Water, and Ice. It also has the coolest shiny, in my opinion at least! It's tail gets a shade of green, and it's shell becomes a brilliant green too. Such an amazing Pokémon!
Finally, at Level 36 it reaches its final form, which is
Blastoise. Defence goes up to a brilliant
100, similar to other starters like in other stats. It's Special Attack goes even higher, so it's a suprise switch. It's just higher by 5 points, though. Not much at all, but still can be important ^_^ It's main stats don't go as high as Charizard, but that's perfectly fine. Physical and Defence are very different! Also gonna mention right now it gets 2 big-ass cannons on its back, which can shoot water that can potentially kill something, according from something I read. Really cool indeed! It's also got a giant shell which can pretty much not be smashed, or any of that sort. :D
So there's all the data about the starters! Really hoped that helped in your choice. I tried to include as much info as I could, I've even tried to give a little insight on my personal opinions on them. I'm happy I could help! o3o~