Both Re and Oleron are ideal places to chill out. They are both quite small - Re is the smaller - and so if you wanted to do lots of sites you'd soon be out of sites to do. Re has a toll bridge whereas the bridge to Oleron is toll free (check this - I'm going on my last visit). This means that you can visit places on the mainland from Oleron without racking up the toll charges.
Re is renowned for its celebrity clientele, and its naturism. It is quite flat and so is good for casual cycling.
Oleron is for ordinary mortals and is full of campsites. It isn't flat, but has a ridge running along its length (not high). The only sizeable village is chateau d'oleron which, like Re's st Martin, is dominated by a huge 17th-century castle. The surf on the beaches on the west side of Oleron is spectacular. The east side, facing Re, is flatter and the coast is muddier. They grow oysters here but if you don't want to be put off, don't look at or sniff the oyster beds at low tide.
A note regarding the spectacular surf: Oleron recieves some outflow from the Gironde river, on which Bordeaux sits - or do I mean s*its......one of the smaller mosaics had a spectacular allergic reaction after a day in the surf, and this may have been caused by pollutants. Having said that, everyone else was fine. But you cerainly get that sewerage pong on parts of the muddy east coast.
http://france-for-vis...lle/ile-d-oleron.html