Which Pokemon should I start off with?

Bulbasaur because the first two gym leaders are somewhat weak against grass moves. Brock you can knock out most of his Pokemon in one hit and Misty is somewhat week against grass type moves. Also, bulbasaur has leech life witch comes handy in bad times.

I would not go with a fire Pokemon first off, because The first gym is a Rock gym and fire Pokemon are weaker against rock. It just makes your first gym battle easier. (So Charmander is a no no) However Charmander is great against grass Pokemon, so if you can catch one of these before your first gym battle and level it up to about lvl 12, you should be right.

But Charmander is a good idea to get if you like fire Pokemon because it is a while before you will see more fire Pokemon in the game.

Either the grass or the water Pokemon will be tough against the first gym. The grass being the easiest to train, and will level up a little earlier than the other two.

I would go with Bulbasaur if you want an easy start to your game, but Squirtle is the best choice, as it might be a while before you will be able to get another good water Pokemon (untill you get a decent rod and.or learn to Surf.)

My suggestion in a nutshell: Squirtle.

My pick if I were going to do it: Charmander.

I prefer Bulbasaur as it has more super effectiveness against more types than Squirtle and Charmander. It will also help you beat Misty the second Gym Leader. But fail against Brock. He can hold it's own against Lt. Surge and ties with Erika.

Squirtle can help beat Brock, the first leader. Ties against Misty evenly but looses to Lt. Surge and Erika, 3rd and 4th leaders.

Charmander could hold it's own against Brock and Lt. Surge. But looses against Misty, yet beat Erika.

Starting off, it'd be best to choose Bulbasaur or Squirtle. But evolution-wise Blastoise and Charaizard can be a sufficient aid.

Think of the Starter Pokemon like this:

Charmander~ advanced players choice

Squirtle~ neutral players choice

Bulbasaur~ new players choice

Hope this helps!

Id go with sharmander because it's pretty strong against most GYM battles as for the first 2 GYM BATTLES just lvl up your Charmander until lvl 12 then you will learn metal claw and for Misty joust catch a pickashu in the vederian forest thingy