I have to have an insulated bottle here in Texas or my water is hot in like 20 seconds! So far, my favorite and the one that I think does the best job insulating is the ThinkSport bottle (made by ThinkBaby which is a BPA-free company that makes sippies, bottles and adult water bottles). It's stainless steel and insulated and keeps water colder than a KK with an insulating sleeve (which I also have). I also find the lid easier to open. My alternate version if I'm feeling weighed down is a Polar Bottle which is BPA-free plastic. It's insulated but doesn't do nearly as good a job of keeping the water cold as the ThinkSport does. But it is lighter. More in depth reviews of adult water bottles on my blog but the ThinkSport is my favorite.
Unschooling mama to one 5 year old DD.