I prefer Platypus bottles because they can be rolled up and therefore take up no space when empty. Of course they're more expensive. On the other hand, it's lots easier to slide a soda bottle into an empty mesh pack pocket. I might end up using one myself if I can find someone to drink the soda!

I read somewhere (don't have the reference now; found it during the BPA fuss last year) that the plastic used in soda bottles is meant for one-time use. It doesn't contain BPA, but it may start pitting (providing hiding places for bacteria) after several uses. Of course if you drink soda you can replace the bottles frequently.
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May your trails be crooked, winding, lonesome, dangerous, leading to the most amazing view--E. Abbey