Hum. I probally like the blue one the best overall. He's not just the most detailed, the actual high-tech asthetic works alot better because of the practical placement of the armour bits, too.
The black/red guy on the far left... Feels like he needs large eye cameras on the side of his head, or horns, or anything just to make his head look less thin, really. Hell, a german helmet-type thing could work. But I wouldn't have said it was that bad of a design anyway. Plain looking, but not, like, horrible.
Keep up the good work Syhuman.