Yellowjacket's my favourite.
I wonder if he'll be in costume in A.I., and which could it be? The fact that the Ant-Man film is being made would suggest that they'd make him Ant-Man, but Scott Lang's in that identity, so maybe that won't be it. We've seen him as Goliath in Age Of Ultron, so maybe they're setting him up to take on that identity again? Hard to tell, how Age Of Ultron will affect things though.
Yellowjacket's the coolest look, personally. He was a little unhinged when he wore it, but it's a nice, simple design - I even like the Ultimate version with all of its detailing:
The Ant-Man and Giant Man suits are nice classics though. Goliath's design is boring, and the Wasp design is one of the ugliest looks with its weird robed appearance.