Hans. He not only has the most effective starting weapon in game, but also awesome jetpack that allows to move across the battlefield and even across the gaps. Only thing that he is missing - is ability to fly up with his jetpack....
Others...
Alicia is the second one, because her shotgun is pretty accurate and fast-fiering. But her special move... well, sucks. You are easy target when you are just stuck in air without moving, and since she need some obstacle to activate jump - it becomes nearly useles.
Lycus has the cool shield that is perfect tool to tank bosses, but his gun is absolute garbage - only few shots, doing just a bit more damage than shotgun, easy to miss, must hit head to do any significant damage.
Shae has the funny ability, but it's somehow hard to use, not obvious enough if it's working or not, long activation. Her gun... i don't even understand it. It's locking on enemies but does nothing but increased damage after full lock, also damage dealt sucks.
Harek is fine. But sometimes his ability buggs and you can't shot, only spy.
Konstantine seems fine too, but he certainly not my style of playing.