It would be a poor idea to go with Charmander, as your team is extremely vunerable to Water moves. However, if you are going to use Charizard Y (with trading), it is a viable choice due to its Ability Drought, which can power up moves for you.
Bulbasaur is average, but you do gain the ability to hit Fairy Pokemon with you STAB moves.
Squirtle's evolution's Mega Evolution (Blastoise) is great in punching holes due to its good Special Attack stat and access to a large number of coverage moves. In addition, Blastoise has access to a lot of HMs, so he can be an effective HM slave.
I would choose Squirtle, but there are more options for Water Pokemon throughout your journey throughout Kalos. If you decide on another Water Pokemon, then Bulbasaur is great as well.