Do you prefer your water bottle to be made of metal, plastic, glass, or something else? Straw or no straw? How big would you want it? Should the bottle taper down in the bottom, or do you think the sided should stay vertical? Are any of you one of the few people who would like that weird rectangular bottle? Or maybe one of those squishy fold up ones for travel? No handle, flip up handle, mug style handle, or little loop?
Note that I am not affiliated with any water bottle company
Depends on the use case. I default to my 1L Nalgene or my metal 0.75L generic metal bottle I got at a museum for daily use whilst sitting at my desk at work. For hiking, I prefer the larger capacity Nalgene (I think 1.75L), and possibly an additional 1L for longer hikes. For cycling, I have a couple squeezy plastic bottles that fit nicely in my bottle cage.
I do like the idea of a glass bottle with the rubber/silicone guard thing and thought about getting one, but decided to stick with Nalgene when I had the replace my old 1L.