In reply to Gazza111:
As with most things the basic answer would be looking for the features that you want, try some on with a bit of weight in them (most decent shops should let you do this) and see what feels right for you. I personally think that keeping it simple is the best way, functional but simple back system, easy opening with gloves on, not to heavy, robust fabric etc. I did have a black Diamond axis 33 but found the back system that pivots a bit fussy and also adds weight and it is thought the guide style zip opening looked good until late I took it to the cairngorm , opened it and it promptly filled up with snow! So now I have a montane torque 40 which I find does the job for me so would recommend that. Deuter, pod, bd , blue ice etc all make good stuff though. You can often pick the torque 40 up for a good price