I don't mind things on my back (I don't sweat much), so I love my CamelBak. I don't like groping for the water bottle - and this is especially important if you're riding with others (by yourself a little weaving around isn't as dangerous).
I maximized the dork factor by getting a hi-viz one from E-bay for $20. I *don't* like that there is zip, zilch, nada cargo space (supposedly there's a way to use D-rings to attach other things... beyond my mechanical abilities), but on 2 out of 3 bikes that isn't a factor.
I like to have the camelbak with water and the water bottle either with Gatorade, or with a "reserve tank" of water - so I can just guzzle at will from the bite valve, knowing I've got the bottle full of liquid of one sort or another.