jaycb,
Water bottles (bidons) are traditional for cyclists. That's how I grew up, not likely to change at this point. Mountain bikers are the new kids on the proverbial block.

Generally, hydration packs are for deployed troops, back-country survivalists and MTB-ers exclusively. Some rugged individualists insist that they can use hydration packs on their road bikes. They are an oddity and will be shunned by the herd. To each his own, I guess, but you've been warned.

Do whatever you want to do. If the pack doesn't bother you, wear it. If it does, make the change to bottles.

For me, hydration pack while riding my MTB, because caged bottles become quickly uncaged when the $#!T happens and you endo over a log and tumble down a mountain side.