Love the concepts

But on the question I would either choose the middle top one or the bottom one.
The top one if he's good the bottom if he's evil. I love red but I have to say they way him look makes him look menacing. I like that.

Hmm... tough decision...

They all have different qualities I like about them. The first blue one is very shiny and I love the contrast in the gold. It's looks kinda like a hero with a wild and chaotic side.
The second blue robot is praiseworthy for it's visual strength and implied toughness. He looks loyal and like he'd survive any attacks. His untarnished armor implies that he's a fresh-from-the-shelf mass-produced model of robot which I say fits him very well.
The third one, naturally, looks strong and chaotic. He looks like he's holding back the urge to pummel his target to the ground. His chest piece looks scratched like he's seen a lot of combat.

Maybe I'm reading too far into this but I think these guys are great.