Judging from what OP wrote, I'd suggest the bigger one that would power the AC. And a quiet one if any way you can do it (used, etc.)
I always aim for dry campsites that are seasonably cool enough or high enough that I don't need to run AC. But I do use my built in Onan for summer lunch stops, rest stops, or for a few hours enroute in a parking lot before it cools off enough turn it off. FWIW I used to do the same when I had the trailer using portable in pickup bed. For me this is the most use I give the generator. I don't tend to use it when camped-I have solar.
