If you think the action in ME2 is clunky, you probably haven't played ME1.
For classes, I think Infiltrator, Sentinel and Vanguard are the best for ME2 - a sneaky sniper with a few offensive powers, a spellcasting tank, and a super aggressive shotgun wielder, all make for very different gameplay experiences. Adept with Singularity is a pretty laid back choice compared to them. Too bad you can only have Liara on your team in the Shadow Broker DLC (I think she's the only team member with Singularity).
Oh and the Soldier is of course a straight shooter, and the Engineer is the least used for a reason.