I own seemingly a million water bottles and have tried most of them for travel. My favorite ones are the Under Armour flip top water bottles (made by Thermos). You can get them in either vacuum insulated stainless steel or Eastman Tritan if you prefer plastic. I usually take the vacuum insulated bottle even though it's larger and heavier because I like filling it with cold water and having it stay cold.

Stainless steel insulated: Under Armour Dominate on Amazon

Tritan: Under Armour Draft on Amazon

Why I usually take it:

- Flip top is easy to open with one hand (straw bottles tend to spew and are hard to clean)
- Lock for the flip top so it won't come open
- Solid construction- doesn't fall apart when dropped or banged around
- Vacuum insulation keeps water cold on the stainless version
- Rubber grip makes it easy to hold, even when full (again, stainless version)
- Has a clip for my caribiner

Edit: if you get the stainless, I'd recommend the plain, natural finish. The paint on the colored version will probably flake off and start to look pretty ugly with heavy travel use.

Keith