The mountain bike shorts are probably the way to go. One thing I would stay away from is the ones with a gel pad, as the gel doesn't breathe. I have a couple pairs of the Novara Metro Gel Double shorts and the pad area gets really sweaty and gross, but the rest of the shorts area breathes great. I just picked up a pair of the Pearl Izumi Select Versa Bike shorts this weekend on sale that I am hoping to try this week. The pad is not gel, so they should breathe a little better. One other point is make sure they have at least some elastic in the waist - some of the MTB shorts come with a belt thing and no elastic, and they don't stay up very well :0.