I actually use both when touring.

I like to carry reserve water in the three water bottles that I carry on the bike while drinking from the water bladder that I have around my waist.

Up until this year my water bladder has been a waist pack. I am seriously considering switching to a standard back mounted water bladder. I need to play around a bit to find out what works best for me on a road bike.

The nice thing is that my waist pack holds two water bottles of water so once I empty it I refill it using two bottles on the bike leaving me with a very clear reserve of one bottle of water.

I find that I drink far more when using the waist pack then I do on tours where I just bring water bottles. Convenience probably plays a major role. I also only put water and ice in the bladder so cleaning issues are much less of a problem for me.

~Jamie N