Depends on the situation. I have Platys, bladders/tubes, Nalgenes, and Gatorade bottles. Each has its own advantages. If refills are required I carry at least one rigid bottle because bladders are not so good for dipping, even the wide mouth Platys. Bladders take up less room when empty but rigid containers are more bombproof. When I'm trying to cover a lot of miles I prefer the convenience of a sip tube. I like containers that refill quickly because water sources where I hike are frequently mosquito sources as well. On waterless trips I use a 1gal. MSR Dromedary. A bombproof container is critical in the desert.

So like most other things, it depends. But after all the experimenting I've done my container of choice is the lowly Gatorade bottle........and the price is right.