Vanguard is weak compared to other classes in ME1, as said before. But if you build him more as a tank with a shotgun, he's still very effective. And then come ME2 and 3. This is where Vanguard shines. Biotic charge is awesome, especially once you have it specced for shorter cooldown and shield recharge with each charge. Because then you aren't a tank with a shotgun any more, but a heavy damage dealing battering ram with a shotgun. Charge -> shoot/melee x2 -> charge, etc. And in 3 it gets even more fun with charge -> nova. The most awesome combo in the game, the second being biotic detonation. (which you can easily achieve with your other 2 team mates.)
So my pick is Vanguard. Once you get through the first game, it's imo the most fun way to play the game.
So my pick is Vanguard. Once you get through the first game, it's imo the most fun way to play the game.