Over the years we have had all different types of water bottles and we have settled on these as favorites. They are easy to use - the water comes out quickly, there aren't any straws, you don't have to bite it to get water out, you don't have to unscrew the lid to drink. They are also easy to clean, but ours didn't really need to be cleaned on the trip...
The adults each had 2 1L bottles and the kids had 2 500mL bottles.