It would be hard to quantify a "best" team but I'd definitely say if you want the easiest gameplay experience pick Mudkip as a starter - it's strong against gyms 1,3,4 and half the team of 7 and only has one weakness fully-evolved, as well as being strong against Team Magma's Fire-types. After that just get your bases covered - I'd advise at least one Grass / Electric-type and another Pokémon with the other of those types' move(s) in order to account for how many Water-types you will end up facing.