I prefer no built-in panniers. I like being able to keep my spare tubes, patch kit, multi-tool, levers, etc. in one of the side compartments and simply put the rack trunk on whatever bike I am commuting on that day. The main compartment is for clothes and lunch, while the remaining side compartment is for wallet, cell, keys, etc.
If I need to use panniers, I just add one of my many sets of panniers...or I just ride the Big Dummy.
I want to know what Jim has against Curt...who seems like a nice enough guy and hasn't even posted in this thread!
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"Let us hope our weapons are never needed --but do not forget what the common people knew when they demanded the Bill of Rights: An armed citizenry is the first defense, the best defense, and the final defense against tyranny. If guns are outlawed, only the government will have guns. Only the police, the secret police, the military, the hired servants of our rulers. Only the government -- and a few outlaws. I intend to be among the outlaws" - Edward Abbey