I have the Hydrapak Flume. This pak just makes sense. http://www.hydrapak.com/
2 great features I particularly enjoy are:
1) the bladder is like a "bag". the entire mouth opens. you turn it inside out and clean it yourself. no more buying cleaning kits/tabs!
and 2) the mouthpiece is a "pull" design. pull it to open, push back to close. the "bite and suck" featured on most camels doesn’t work for me. trying to bite and then suck when you’re winded is a pain.
hope this helps someone looking for a good pak!