When I go on any ride over 50 miles, I bring my MULE, and 2 waterbottles. If its really hot, I'll stick a couple more bottles in the backpack giving me roughly 180oz of liquids.
Its not uncommon for me to empty my 100oz CB in under 3 hours so obviously waterbottles alone isn't gonna cut it for me. Since I drink so much, I glad to have the bottles for backup but my primary will always be the camelback.