I have a 15-year old Camelbak MULE. It was the standard back then, and it's held up very well. Think about what additional gear you'll want to carry, and then, make certain that whatever you choose can handle that gear without splitting open. Normally, for a long day during which I anticipate weather changes:
- 1 change of outer layer
- kit for tire/tube repair (pump or CO2, tube, tube repair kit, tire levers)
- snacks
- keys, wallet, phone, etc.
- kit for all other mechanical issues (derailleur hanger, spare chain links, quick-link, zip ties, toolset)
Enough water? That's a judgment call. Will 100 ounces be enough? Usually, yes.