Well, for starters I really wouldn't worry about the bamboo not lasting. Other than the binding on the older One-Size, there's nothing concrete to say that bamboo would last any less than cotton. Lots of people speculating and worrying about normal stuff (probably prompted by the binding issue mostly), but nothing anywhere near concrete or real. It's up to you of course, but I personally wouldn't let that factor much into your decision.
Theoretically organic cotton will probably not last quite as long as the regular cotton as polyester does add strenght and durability to the fabric. BUT that doesn't mean that they'll fall apart quickly. Far as I know, durability isn't really an issue though...
Anyway, not sure how much that helped but thought I'd throw that in there for consideration... Hard decision I know, depends on so many things... I'd say keep using the ones you have for a while and see which you end up reaching for more often when they're all clean.