In reply to Dirhaelar:
You might think I'm mental but an OMM classic 25l.
Why?
It's primarily designed for running but the features on it allow for all round mountain use.
It's reasonably light but still strong. The ripstop does last longer than you'd expect. Obviously thrutching up a gabbro chimney is going to shorten it's life somewhat. I've had one for around 4years, run 4 LAMMS plus all the training, taken it cragging, taken it to the wall, been winter hillwalking, etc etc.
But that said if you want something more bombproof( but more simple/less versatile) the Warthog 26l is brilliant too. Not sure I'd want to run with it though!