I think you have to figure out what works best for you. Standing can be a great way to relieve pressure on the "hoo ha" , give muscles used while sitting a break and make use of some other ones. Yet, those "other ones" need to get into shape for this, plus it takes more cardiovascular strength to stand.

My husband is an avid climber. He loves it. WhatEVER!!! Anyways, he's all for standing, but doesn't do it the entire way up a long climb. If it's a short climb, he'll usually stand all or most of the way. If it's a long climb, he'll do a little of both for the above reasons. He trains his legs to do both and gets the most out of them this way.

I love standing on a climb, but my lungs can only take it for so long. I have to be very careful how long I let myself stand. Otherwise, I get so out of breath that I can hardly finish the climb even if I sit back down. I find, for myself, sitting and taking it somewhat easy is the best way to get up a long climb for me. I usually only stand if it's relatively short. I love coming down a hill and going back up another one standing to keep my momentum going.

Hope these tips help!