Resistance, here. Although, as I said in one of the numerous other threads, I'll be playing Security a lot as well, considering what side you're on affects what side of the campaign levels you play. So, for variety and to experience the complete game, I'll be playing
both sides.
For both looks and politics, though, I like the resistance. As The Zero said, badass underdogs. And I also share RaaiKKen's stance that the Security seem like bad guys. I know they're not bad guys, and that's left open to interpretation, but I just feel more of a connection to the Resistance. Although I actually like how the Security looks too, just in a different way. Basically, Brink rocks, Resistance rocks, Security rocks, and I'd be happy either side, but am more interested in Resistance.