General suggestions:
Personally, I wouldn't buy any backpack without trying it on. Take some weighted items, or the stuff that you would like to carry in it, and try it on again. A lot of the new padding is great, but sometimes the contoured shapes don't fit the contours of all backs. It's all very personal. Anymore, I wouldn't even worry about brand names if it comes from one of the major brands, so many of them are made in the same factories. If you can buy from a company that makes their own bags, that would be a plus IMO. Look for quality materials, sewn well, with good zippers. Make sure all the stress areas are bartacked or otherwise reinforced. Decide if you want a lot of smaller pockets, or one big bag. Try to check out the company's warranty.
That doesn't really tell you where to find the perfect bag, but those are some of my criteria. I have a Jansport daypack right now that I like a lot and is well made. Several years ago I wouldn't have bought a Jansport unless it was to give to a kid for a book bag.
Isn't Crumpler an Australian company? I don't know much about them, other than they look funky and seem to have a lot of buzz lately.