I've had a macpac pursuit for almost ten years now and it's still going strong. I don't think that you can go wrong with Macpac personally exceptionally tough, mine is still totally waterproof, and I find that at 45 litres the pursuit is big enough for me to use as for a couple of days winter climbing, and also cinches down to be comfortable when half empty.
I can get my buffalo bag into the bottom, with a bivvy bag have room for food and kit and get a rope stashed accross the top.
Otherwise I hear that the current crop of berghaus sacks are getting good reviews.
Best of Luck
it's a lonely old world..........if you try hard enough!!