Just about always go for the most RAM you can afford - I say that as a happy 8GB owner, because it's good advice. My 15-inch M3 MBA is absolutely fine for all the things I do with it, so no complaints about the lower RAM capacity, but I knew it was sufficient for the things I was ever going to do with it.
But unless you are really unhappy with a 13-inch screen (I was, because it's not large enough to work with my declining eyesight) the smaller screen and larger RAM is the better way to go.