Avignon for 3.5 days. Most important to see?

We enjoyed Pont du Gard...Aix was OK (we were there on a particularly rainy day, so didn't see a lot). Of Arles and Nimes, we enjoyed Arles a little more. Rousillon was lovely. If you like historical towns, Les Baux was quite interesting.

That's a great time to visit. But Jennifer, what do you like?

"Most important" implies some kind of formal Hierarchy of Culture, but your tastes should rule the day. My suggestion is to read few good guidebooks and see what jumps out at you.

I don't mean to be coy. Some highlights in Provence are the Roman antiquities and the hill towns of the Luberon. But maybe you don't care for that, and that is okay. For my part, I would not stay in Avignon for a trip like this, but it may be just right for you.

Having a car is a great idea. You will be able to cover a lot of ground in your 3-1/2 days. Have fun!

After seeing the highlights of Avignon, we enjoyed going over to Pont du Gard one day. Rent a canoe to go under the bridge. We also spent an afternoon at Nimes to see the Maison Carree, the Arena & the Garden/Park with the Temple of Diana in it. A third day we enjoyed an afternoon of the Luberon villages & a lavender field.

We enjoyed walking the central pedestrian area of Avignon each morning/evening. Our hotel was very close to the carousel.

Just an FYI - we didn't rent a car. Took a bus to Pont du Gard, train to Nimes, and a mini-van tour (picked us up at our hotel) of the Luberon villages.

I visited Provence in May for a few days, without a car. I stayed in Arles, not Avignon. People (including Rick) rave about Arles, but I was not impressed. It was really dead both nights I was in town (Sun and Mon nights). Not all the restaurants were even open at night. I really wished I'd based in Avignon, which wasn't amazing and was a bit more touristy but still had a nice vibe to it.

I day tripped from Arles via Avignon to Pont du Gard too, via bus. It was pretty easy, but the bus schedule in May (perhaps also in September?) was pretty limiting. I wanted to try to squeeze in a trip to Uzes (same bus line as Avignon to Pont du Gard) but just couldn't work it out without limiting time somewhere. I wanted a lot more time at Pont du Gard than expected. The museum there is really nice and takes time to see, and the walking tour inside the bridge is by guided tour only and only at certain times in English.

I had considered renting a car. I think it would have made seeing some of the little towns in Provence a lot easier, but it seemed pretty expensive, at least by the time I got around to checking rates, so I didn't bother. And to be quite frank: I wasn't as blown away as so many of my friends seem to be by Provence, so I don't necessarily regret not renting the car anyway. But if the OP is willing to rent the car, I'd probably do it - it will make things easier.

Arles is definitely worth a visit though - lots of interesting, worthy things to explore, just not a place I enjoyed spending the nights.

My husband and I loved Pont du Gard and the Nimes Arena. All the towns/villages I saw were charming, so what I recommend is going to whichever one has the local market on the day you are exploring. The first market I visited was in Bedoin (at the foot of Mont Ventoux) and I was awestruck. It was a feast for all senses and one of my favorite memories of 3 weeks in France.

Carriers des Lumieres, Roussillon, and Arles are my favorites. Tapenade and Brandade are my favorite foods.

I'm planning similar for later in September. I'm interested in history and older architecture (17th century is too new for me). I also like geography. So my list for the area includes, Pont d'Arc, Ardeche, Orange, Uzes, Nimes, Pont du Gard, Avignon (but I'll primarily focus across the river on Villeneuve and take a ferry across for only a quick look around Avignon), San Remy/Glanum, Les Baux, Arles, L'Isle sur la Sorgue, Gordes and Abbey Senanque.

I typically design logical swaths, to the extent possible, so I don't spend too much time backtracking.

I'll be there about the same amount of time as you. I'm coming from the north, so I'll start from where I'm staying (up by Balazuc), then Ardeche (north to south), then Orange and plan to end at Pont du Gard before heading to Arles to check in for three nights. I might add Uzes, Nimes or Avignon, depending on how the day goes. Ideally, seeing Avignon this day would eliminate the northern most stops for me.

Day two (after night one) I'll start at Nimes and pick up Uzes, if I haven't done it, St. Remy, Glanum, Les Baux, and Avignon if I have time, again just depends on how much time I'm spending at each stop.

I'd rather drop a few stops than skip my must sees where I do stop (but I often know what I want to see, have a map image in my head (and a GPS), and my normal walk is most people's hurry.

Day three (after night two) I'll either start in Avignon for the morning, then head east toward the Luberon area or just go straight there, if I'm finished with Avignon.

Day four (after night three), head toward the Riviera. I'm leaving the Luberon sights for last. If necessary, I'll make stops here on the way toward ending the day in the Riviera (where I'll stay four nights because I really love the ocean, even if it isn't beach weather). If I've made the stops I want, I'll stop at Aix enroute.

Just a tip about a wonderful restaurant in Avignon...Fou de fafa. We were there last fall and it came highly recommended and does not disappoint. Luckily we got in without a reservation, as it is a very small, cozy place. The chef and his wife are from England and have made quite a name for themselves in Avignon.

http://www.avignon-tourisme.com/home-1-2.html
The Avignon tourist office is among the most helpful I have used in France, both at its central location and on-line. It has plenty of suggestions for the region. I liked the ampitheatre at Orange, with a side glance at the Chateauneuf-du-Pape although the chateau itself is a pile of rubble, but yes there is wine to be had. https://en.wikipedia.org/wiki/Ch%C3%A2teauneuf-du-Pape
And Arles is always a worthwhile side trip, with two ampitheatres and a tasty (although occasional) farmer's market. Avignon's own municipal market will make you hungry for lunch -- daily except Monday but in the morning only.

Just returned from a week in Provence.
Arles and St. Remy (drive from arles to St. Remy scenic drive) for all Vincent Van Gogh..(the Liberty pass in Arles is a good deal if you want to see 3 or more sites) . Les Baux and Carrieres de lumieres (quarry) were a great stop.. do Les Baux first early in the morn and the quarry second (buy the combo ticket) If you hate art then skip Arles and the quarry, but if you love art then be ready for a quite an experience in the quarry. Be it known that you don't have to do everything on the same day., the liberty pass is good for a month as is the combo ticket for Les Baux castle and quarry. We stayed near Roussillon, definitely worth a visit!!!! Don't bother wit Isle sur la Sorgue.... . The Camargue was very different from the Luberon. Pont du Gard was interesting to see but we did not spend much time there as it was very hot.
We had dinner in Fontaine-de- Vaucluse .... a very lovely small town in Provence.

Look for a good market at least once while you are there. I wish I had purchased more goodies at the local markets.... Very fun!

I just returned-
My advice is to prioritize some quiet time to just wander some of the smaller villages, perhaps explore an open-air market. You will appreciate the experience of just being in France, which you can miss by trying to visit too many sites.
I personally liked Avignon and Roussillon the most.