First Trip to South of France - Seeking Advice

I stayed in Arles in April this year for seven nights and we had a car so access to the surrounding towns was easy.There is the Amphitheater and Coliseum and market days along with a good museum of the history of the area.Lots of good restaurants within walking distance of hotels.
Mike

Nice has quite a bit of interest, more than Cannes, on my opinion. From there, you have fairly easy access to a number of towns. St. Paul de Vence and Eze immediately jump to mind, but there are many others.
Arles would make a good 2nd base. There is much of interest there and in the surrounding area.

Rail service to the coastal towns on the Riviera is generally good and allows you to avoid the traffic on the coastal road. You may find a car helpful for the villages up in the hills, but you'll need to select your Nice lodgings carefully with respect to parking options. Nice is a large city; I wouldn't want to drive from sight to sight within the city.

You'll have time to see a lot of things in southern France, but not everything, so pick up a good specialized guide book to the area (Rick has one) to help you prioritize.

You'll find some good tips in this recent thread: https://community.ricksteves.com/travel-forum/france/provence-in-6-full-days
Also, entering something like "Luberon" or "Provence Villages" in the Search field above will produce more. We were pleased with L'Isle sur la Sorgue as a base in 2016, but it's hard to go wrong in the region.

It should be nice enough along the coast the days the Mistral wind isn’t blowing, but the interior can still be cold and even glacy when the Mistral blows. These winds come out of the Alps about every third day. The further east you go along the coast, the nicer it is in March. Menton has a nice, warm micro-climate. Between Nice and Cannes: Nice.

We rented a small gite at the south end of Saint-Remy a couple of summers ago, and it was ideal. The town's a great size - definitely not too big, but it's still big enough to offer essential services to travelers like a decent food market, shops, bakery, glace/gelato, etc. We made driving day trips to Arles, Avignon, and Nimes, as well as visiting locations closer to Saint-Remy itself.

I've had an apartment in Nice several times. The neighborhood by the port is a great location, a couple of blocks from the end of the Promenade des Anglais, close to Place Garibaldi square, great transportation access to the Tram, and outstanding restaurants like the Italian-French Café Alto, and upscale L'Uzine, and of course Chez Pipo for socca.

We've rented a gite for a week twice in St. Remy, and thought it was a good base (at least the time that we had a car). There are plenty of villages in the area worth seeing, and the town has plenty of amenities.

I rented a lovely gite just outside Fontvielle. I enjoyed seeing Arles for a day, but I was very glad I did not stay there. I liked the amphitheater in Arles (although I found Nimes' more impressive) and the museum with the Roman barge was fascinating. But the city had a "blue collar" feel, which is not what I was looking for on a holiday. Have you read Rick Steves' guidebook re Arles to hear his thoughts about the atmosphere there?

In contrast, Fontvieille was a centrally located to what I wanted to see as Arles but was picturesque, quaint, and peaceful.

I like Avignon, well located for transportation, day trips, even an airport connection (local train to Marseille Provence airport). Its travel bureau is very helpful, both for its own city and the region. http://www.avignon-tourisme.com/home-1-2.html

If you head further west in southern France there are some beautiful areas that are a bit less touristy. We have based in Herault in the town of Pezenas and explored that area. There are MANY wineries, small villages "circulade", beaches, castles, etc. Pezenas has an amazing weekly market and you can easily explore something different every day by car. We particularly liked Beziers, Narbonne, Montpellier, Coulliore, the Cevennes, St. Guillaume le Desert, and quite a few of the wineries! Our favorite of those was Abbaye de Valmagne not far from Pezenas. It's in a former monastery and the giant casks of wine are in the side chapels of the former church - unique and lovely!

As others had posted, for the Cote d'Azur portion, Nice over Cannes. It's more central and better connected, with a greater variety of choices. You really only need a car if you are going into the hills at that point, except for St. Tropez. I would stay central, somewhere in the area along the tram line to the main Nice Ville Gare, in the Carre d'Or, or in the Old Town (that is the toughest with parking). At least some of the lots have weekly prices for a reduced rate (but you must ask in advance).

Did an AirBNB in St.Remy. Great town. Lots of stuff open late for a small town. Always nice to come home and take a nip around the block for a drink or ever dinner if you are lazy. The Wednesday Market is fantastic. Really loved that town. Has a huge supermarket on the edge of town for supplies and wine.