It's worth knowing what your options are before you head down to the seashore and throw your towel in with the punters on the public beaches. For one thing, you'll not be throwing your towel, you'll be carefully unrolling it on one of the patches of scalding pebbles that is not yet occupied, and for another, you'll need to keep a careful eye on your gear when you go for a swim (not an easy feat when negotiating the Med's punchy little waves). Unsupervised bags are easy pickings for opportunistic thieves.
Going private can eliminate many of these hassles (lockers keep your belongings safe, thick hessian carpets lead right down to the water's edge, protecting your feet against the tricky terrain). But the options vary, and some beaches are better than others. It all depends on what you're looking for (and, of course, where you're staying, as a good many of the hotels have preferential rates with various private beaches).
Opéra Plage offers a smart spread with the addition of a locker for valuables.