I just noticed I had unknowingly purchased different spare tubes. The tires are 26x1.50 Bontranger H2's used 100% for 'round town riding.
I have some spare tubes spec'd for use on 1.0 - 1.5, and others spec'd 1.5 - 2.0.

I'm wondering which would be the better tube choice, in general. There's just a little more material on the larger tube,I would expect. If reducing probability of flats is the goal, which is the better choice? Or doesn't matter much?

doesn't matter

I use 1 3/8 tubes mainly just for making it easier for getting tubes into the tire

The tubes in all 3 of my bikes are sized according to the tire size. The tubes I carry in my tool-kit(s) are all undersized for ease of roadside replacement. Reduces the chances of having a pinch flat. Then I repair the original tube when I get back home and deflate the replacement tube placing back in my tool-kit.

All of my 700c inner tubes are 23mm; doesn't matter if they are in a 28mm tire, a 35mm tire or a 42mm tire. I got a good deal on a wholesale lot of inner tubes, and I've been running through them ever since. It doesn't make a bit of difference.