I don't want all the weight on my back. For my tour I will have three 28 oz bottles on the frame and then two dromedary bags. I haven't decided what size I will get. Most likely I'll buy two 4 L bags. They're indestructible and collapse down great when not filled with water. I chose to use bottles because I don't want all the weight on my body while riding. I sweat a lot so having the amount of water I need on my back makes no sense to me.