The first rifle definitely has a fun design, but the second's silhouette feels weird... maybe its that fore grip. Since the weapon has a bunch of attachments on it already, go ahead and just make it another accessory, aka, have it attached to a tac-rail and move it back some. It looks like a bit of a reach.
Ironically, I love the ergonomics of the third weapon. The stock, the grips, the sights, its all looks very streamlined and comfortable.