It depends on your riding style. Do you like to sprint or cruise?

Personally, I'd go with the 700x38 (or even smaller). Unless you have really rough pavement anything wider than 32 is going to provide plenty of cushion. A wider tire also gives you better puncture protection, but again I think 32+ is plenty good and additional width doesn't provide proportionally more protection. For these reasons, I'd go with the weight savings of a lighter tire. I know weight isn't supposed to matter for a commuter, but to me heavy tires just feel sluggish.

On the other hand, a tire like the Marathon Plus is not going to feel either quick or plush in any size. They're a great tire for puncture protection, but I can't imagine loving the feel of them in any size. As such, my argument for the narrower size isn't really applicable. I'd probably still go with the smaller ones.