I purchased my Camelbak Helena 20 pack in 2012 and I love it. I haven’t used it recently, but it’s still got it’s own hook in my gear room. The Camelbak reservoir was the standard one that comes with all their packs: plastic, 2-liter, circular twist opening with little kickstands for drying. The hose was the normal plastic one with the yellow bite piece and open/close toggle.
I used this reservoir exclusively for four years. It started the AT with me. It then, inevitably due to the heavy usage, sprung a leak and soaked my pack. I fortunately had lined my pack with a trash bag and put all my items in there (I’ve since upgraded to a heavier-duty trash compacter bag). I patched the leak with duct tape. Then there was another pin-hole leak, then another. By the time I got to Damascus, Virginia, the reservoir was probably a quarter duct tape.
I went to Mt. Rogers Outfitters in Damascus, Virginia, and purchased a MSR Hydromedary Bag, 2.5 Liter reservoir. I love it. The material is more flexible and forgiving, the opening is much easier to work with, and it just seemed to fit my bag better. I also like the bite piece more than the Camelbak; it doesn’t seem as flimsy. It lasted me the entire rest of trail and backpacking trips since. When it finally dies, I plan to buy another MSR reservoir.