I have quite a few Nalgene bottles and Kleen canteens, some I've bought and never used. The ones I stick with now are 32oz clear Nalgene bottles and 18oz single-walled stainless Kleen canteens.

I like the Kleen canteens for belt carry, as they're a good size for that, and if it somehow ends up being the only water bottle I have, I can use it to boil water in.

The Nalgenes I like for general water carrying. Because they're clear with graduated markings it makes it easy to see exactly how much water you have left. This is great for cooking as well (measuring out water is easy).

I've also equipped the Nalgenes with Guyot designs "Firefly" lids. I find these seal better than the stock Nalgene lids and they have a neat little function of a built in flashlight that turns your water bottles into a dim lantern (or a so-so back-up flashlight if worst comes to worst).

I've tried camelbacks in the past, but I've never really had good luck with them, so I don't trust them.

Now, I also have a little 8oz single-walled stainless steel flask that I carry, usually filled with Booker's bourbon...but that's for another topic of discussion.