Definitely Colossos. Balder was a massive let down, and I cannot understand why anyone rates it so highly.
Colossos delivers exactly what it's supposed to deliver - amazing, sustained ejector airtime on multiple hills.
Balder never really seemed to hit its stride, and I don't rate it at all. The ride doesn't deliver enough of a punch on the bigger hills where it could actually have sustained some airtime, and the pops of ejector airtime on the later hills are so brief they're over as soon as they begin. I wasn't expecting amazing things from the ride, but even with my limited expectations going in I was left massively disappointed. I'd rather have a mega-lite any day.