I like a mix of water containers. A 1- or 1.25 liter plastic pop bottle fits well next to my tent on one side mesh pocket of my pack, and I generally carry a 20 oz gatorade bottle on the other side. If carrying a lot of water, I make sure that these are full, so that all of my water weight isn't at the top of the pack, putting me a bit off-balance at times.

I too use a platypus as my go-to water container as I use a drinking tube. Beyond that, it's a Nalgene brand 3-or-so liter "cantene" (made for hauling/storing a lot of water). I used to use a platypus brand water carrier instead, but just never trusted the zip-top. The Nalgene is harder to pour from, but it's pretty bullet-proof when full.

At one point I bought two 1-liter platypus units in little neoprene sleeves that had belt hooks, and put one on each side of my backpack waist belt. This was intended for the dry southern part of the PCT and they seemed to work well on a couple of shakedown hikes. The idea was to carry some water weight directly on the waist belt and at a lower center of mass.

Catch was, every time I would sit down, these would unhook and I always seemed to be fiddling with them, so they pretty quickly got sent home once I started on the actual trip.

I've heard people suggest not using platypus (or the equivalent) because of all the needles and thorns in "the desert". My tentative conclusion is that these folks were carrying them externally. The only water containers I carry externally are the pop or gatorade bottle type, and I've never had a platypus leak, FWIW.