spinning uses more anerobic (sp?) while gearing up (harder gears to pedal) uses muscle power. There is no right or wrong anwer to this because it depends on the rider and to be frank, its a tweaking thing. For me, with my weight, its much easier for me to drop down some gears and spin and when I go up hill, I am just slow and I am ok with that. Climbing for me I think comes down to 1) pacing myself 2) pulling up on the pedals on the up stroke 3) breathing pattern and 4) keeping my mental voices in check which usually means keeping my head down and focusing on the "now" and not how long I still have to do on the clib.