I've used a USGI canteen for years just because it was given me. It is very rugged and extremely thick and heavy. The one thing that I really like about it is that I have the SS cup/pot that fits on the bottom of it and that I can cook in.

For a lighter weight system I plan to go with a Nalgene and one of the SS cups that fits on the bottom of one like this:
http://www.campbound.com/stainless-steel-bottle-cup.aspx
The cup will be smaller but I am ok with that because of the drastic decrease in overall weight.
I will probably also get a hydration bag to carry extra water on longer hikes. The main benefit that I see with them is that they are so compact when empty.