I think it depends on the sort of holiday you want. MW is an Uk company designed to handle Brits and their needs so if you fancy a couple of weeks with a selection of people from your local school and gym, eating English style food etc then you will prob enjoy MW.
CM is a french company catering for a lot of different nationalities (Germans, Dutch, Italian, French and UK) with a main working language of French and meals are informal but important affairs. You get a well stocked baby feed rooms with water, milk, fruit, yogurt etc, a children's restaurant open at 6pm, pushchairs and beach umbrellas on loan. There is nurse on site and a peadiatrician visits each evening, I think.
If you intend to leave your child in the creche for a couple of hours in the morning and afternoon I think the creche is fine, my 10 month ds was quite happy although the staff ratios are not as high as MW. I'd never left my child in a nursery-style situation before and I didn't feel that holiday was a suitable time to try leaving him all day.
Metaponta is a big site with lots to do, MW would prob fit into a corner of it. The Hobie Cats on the beach were great fun to sail although I'm not allowed to try rollerblading anymore (I broke my wrist at my first lesson despite wearing all the kit). We went in June and soon realised that we didn't need to spray ourselves against mosquitos which was a pleasant relief (between us we are usually a fine dining experience for the little critters). We could also fit the cot easily into the bathroom, do make sure you ask for a baby bath.
MW is prob the more watertight experience for anglophones, partic if you want things to run the way they do at home. CM is more of a foreign experience, CM Ibiza might be less of a challenge with a small child (the transfer time is much shorter aswell).