In terms of weather and likely rentals the Med is better than North Atlantic. (Wind is stronger along North Atlantic and others have told me weather isn't as good there.) The further South you go aong the Atlantic coast the better. Places like Agadir have proper 12 month seasons, but the flying time is longer.

If you are limiting your search to the coasts then I'd suggest Plan Azzur developments, with all the amenities they offer, are a safer bet than smaller developments (unless a big player like Emaar ot Fadesa are behind them.) For now only Saidia (Med) and Port Lixus (North Atlantic) have had prices launched. Essaouri could well be the pick of the bunch. Everyone I know that's been there raves about it. The same can not be said for Casablanca, Agadir or Tangier