Adept is way better in Mass Effect 1, Vanguard is better in Mass Effect 2/3 due to the awesome Biotic Charge although Vanguard does allow you to equip Medium armor.
I just played ME1 as an adept - and rolled it into ME2 - I thought I would, for once, try to stay with a class all the way through. Adept in ME1 was kinda meh, though by the end, yeah effective enough, it just had no oomph. But I stuck with it - singularity in particular was hilariously overpowered high up int he skill tree - I'd just toss it any old place, and crates, mobs, rocks... all would get picked up. ME2 biotics are just so much more satisfying. Throw just makes me laugh so often, looking for mobs I can nail so they go flying off a bridge or whatever. Heh.