PalenQ

No but have been to source of Loire - way down near St-Etienne so way out of Orleans where I once stayed a lot.

shamouel

About the climate, every week may be different : you may have a very beautiful spring period as well as a rainy and windy one, regardless of the region you choose in northern France. Brittany and Normandy have very close climate (even usually warmer and oceanic in Brittany), and not that different from the one in the Loire valley (the Loire valley is cooler in winter, warmer in summer).

Gardyloo

When in March? In the first half of the month the weather is likely to be crappy everywhere you've mentioned, so the options (in my opinion) would be (a) go someplace with a better chance of decent weather, meaning south, or (b) choose a place with plenty of indoor activities. Some years ago we visited the Dordogne in late March and were stymied again and again by flooded rivers and closed roads. On the other hand, the Cote d'Azur and Languedoc are likely to have better weather, maybe even sunshine, and there's no shortage of interesting or historic things to see or activities to experience. You can get from Paris to Aix en Provence in around 3 1/2 hours on the train, or to Montpellier in about the same time. You could explore the Camargue including Aigies Mortes, the stunning coastline between Cannes and the Italian border, Cathar castles or Roman sites like the Pont du Gard or several around Nimes, Provencal hill villages... the issue will be what to skip rather than what to include.

PalenQ

Yes in March I too would urge taking train to say Avignon for nice weather and a spring that has sprung - rent a car and stay in a smaller town like St-Remy-de-Provence, a favorite amongst Fodorites.

StCirq

March is normally the absolute crappiest weather month in France, so yes, go as far south as you can get. Gardyloo's experience in the Dordogne in March mirrors our own, living here, for the past 3 years. We hate March.

I'm no fan at all of St-Rémy, but loads of people love it, and there are many other lovely choices not far from it, like Uzès.

PalenQ

And maybe in March cities are better to base in - Arles is a really neat smaller city than Avignon - both ooze old-world charm and if did not want to rent car you'd find local public transports sufficient to do a few day trips or take organized tours. Did not realize March was funky too in Dorodgne but probably a better funk than Loire Valley or northern France.