On a journey from Levanto Italy to Barcelona Spain, I will be taking my students to Provence region for one night before departing for Carcassonne. Where would you rather stay/visit (short visit!) Arles or Avignon?
I would choose Arles. It is fairly compact and you can see the area inside the walls in a short time.
I would also choose Arles. I prefer the ambience and the size of the city is more doable for one day.
If your trip is in July, Avignon has a large music festival that, from what I have read, brings crowds and sparse hotels.
I've been to both, and I usually stay in Arles. We make Avignon a day trip, but Arles is a tighter, more compact town that is really delightful in the evening. That's the one that I'd pick.
Thanks for your suggestions - Arles it is! Now to find a place to stay... with 50 other people.