We are members of both but the advantage for us of the C & MC over the C & C C is that as we don't use the shower in our Troll we use the site showers a lot.
It does seem that many caravan & motorhome members use their own facilities whereas the large number of tenters on C & CC sites means that the showers and toilets seem to be much more busy, with a tendency to you having to queue more.
MikeT