It all depends on your play style. If you Run & Gun, the Jetpack would be more efficient in surprising opponents in the middle of a gunfight. If you play tactically with your friends, the regen field would be a better choice as it would heal your whole squad. The Hardlight Shield is also effective in teamplay, as you can use it to be a distraction and your buddies can come in and sweep.
I love the Thrust Pack. It really is useful when you're trying to escape enemies who are chasing you. However, I mainly use it to boost myself behind an enemy who is tailing me: it really throws them off.
Mafia vs. Irish Mob (BROTHERHOOD series) http://www.youtube.com/watch?v=4C-ogMPoBRk