Venusaur:

Useful for catching pokemon. Let Venusaur learn status problem moves. Venusaur is not that great in battling. Bulba-Venusaur is worth alot in the GTS. Put one up for trade for a Squirtle, Charmander or other starters and you have a high chance of getting it.

Overall rating: 3.5(5 is the highest).

Bulbasaur-Ivysaur-Venusaur

Charizard coming next.