I always buy lightweight tubes in the size range that has my tire size at the upper end, or maybe even a little smaller. I think the ones I use in my 23's and 25's have a range something like 19-23.

I just find it easier to use a slightly smaller tube than to try to stuff a larger tube in there.

Plus, although I have no proof, I believe that it is not the tube that is vulnerable in flatting, but the tire itself. I therefore have gravitated toward lightweight tubes, somethimes marked "ultra light". Another reason I go with the smallish, and lightweight tubes is that they are more compact and I like to use a very small under saddle wedge pack. With a small tube, I can get it, a patch kit, two tire levers and a multi tool in almost the tiniest pack available. I don't go with the most expensive, super lightweight ones, just because of the cost.