If you're really into it and can spare the cash, the French made Resurgence Pack is the top of the line. http://www.canyonsandcrags.com/servlet/ ... cks/Detail
. I have had a Resurgence pack for quite some time and it fits the bill for a rugged pack specifically constructed for canyoneering. Whatever you decide on, I think the important features in a good canyoneering pack are durability, construction to allow drainage, a minimum of exterior straps and pockets that can snag on things. and comfort (critical if you do canyons with long approaches).