I was using two water bottles for long rides of 2+ hrs but have switched to using a Camelback. I pack it full of ice, put a touch of OJ into it and 40 oz of cold water and the fluid stays icy cold and refreshing for a long time. The touch of OJ adds a bit of flavor and is nicer (for me) than plain water which tends to taste musty or like plastic either either the Camelback or water bottles.
What do you guys use? Bottles or Camelback?