Unless you're going to use it a lot, I can't see the point of either!
Both have serious but entirely different downsides.
Caravans have to be towed to site, which compromises the journey there quite badly.
Motorhomes require you to pack up every time you need transport, and I cannot see the attraction of driving halfway acrosss the country just to sit on a campsite for a few days! Plus, you have another vehicle to pay for, and it's only good for sleeping in; a properly converted one is no use as a van, even if it started off as one.
Buying either isn't cheap, and you need somewhere to keep it, which is damned costly.
Surely the best way to decide if either is for you is to rent a motorhome for a few days, and use it for the sort of trip that you have in mind. Personally, when you add up all the costs and problems then hotels or decent B&Bs are the way to go.
As for camping, I hate it. That's based on several years summer holidays as a kid when it was enjoyable, and 2or 3 weekends at selected shows over the last 14 years. I only camp at those because they're normally held in the middle of nowhere, and the 'socialising' -the real reason for going- continues into the early hours and makes driving impossible.