I stand for most of my climbing. I heard at one point (Dont know if it is true or not) that those with stronger upper torso's feel more comfortable standing and those with stronger legs sit. I do a lot of climbing and have recently found myself doing more of a 50/50. Switching positions between standing/sitting and different hand positions to not burn out as early. We have several hills around here that are good 15-20%+ grades that are 2-3 miles long. (really gets those legs burning)