Just wandering by the water isle in the local supermarket I noticed there is a wide variety of water bottles to choose from.
I like that there is quite a few with "clip in" rings on the top. -Saves you all that time making little clip in loops yourself for each bottle.
My wife prefers the 1.5 long thin bottles because they tend to crush easier. also if any bottle breaks you don't loose so much.
If you can find bottles that have a wide mount it's nice for ease of adding sports drink.
So look for: clip in point, wide mouth, and crushability.
Happy big walling!
Hans