In reply to billb:
As the OP still hasn't answered a few of the key questions... we can only give our non fact based opinions.
The key questions, that require answes are:
1) will you be climbing with it? If not, perhasps a crag-sack is an option.
2) is the walk in short or long? If no climbing with the sack and short'ish approach perhaps a small basecamp duffel, small haulbag or crag-sack is the way to go.
3) will you be using it for also hiking and so on?
So, the "best" sack depends on numerous things... and can vary from expensive 'Ryx rucksack (Alpha FL45) to 1 quid Ikea bag (if you don't steal the shop one).
For what it is worth.
A bag I climb with one of these 3, Warthog 26l, old c. 35l 'Ryx Cierzo or c. 55l Virga 2. Which sack, depends on the route and what I need to bring with me.
For craggin' with a walk in, it's generally a small c. 60l haulbag or DMM Vector (rigged to also suit ice tools).
For crags, with minimal approach, it's the Ikea 1 quid bag.