Wow, you're world apart here. Rocamadour is in the Dordogne, full of tourists, a bit like Lourdes. The Carmargue is about as far south as you can get before you drop off France and not full of tourists. Mostly it's empty, apart from the birds and wildlife. There's nothing similar. The only thing you can say about them is that they are both in France. Having said that, I wouldn't go back to Rocamadour, but we go back to the Carmargue regularly.
You'll get people who recommend Rocamadour, which is OK if you like following half the world up a hill full of tourist shops to a shrine at the top, or the bottom, depending on which way you're going. The Carmargue is wild, especially off the tourist routes, full of wildlife, wild rice, wild bulls, wild horses, and wind. St Maries de la Mer is Gypsy Town on Sea, but worth visiting, (and the Carmaguais bullfights where no bull gets killed are spectacular - and sometimes free at St Maries de lar Mer), the bird sanctuaries are amazing, you can drive out to the end of the world - and have the mediterranean on both sides, and you can eat seafood to die for. I know what I'd go for - but you'll no doubt get others who argue on the other side.