If it's a good restaurant and the food draws in customers, it can be a gold mine. A car wash won't make you as much money, unless it's a large enough operation. In all actuality, though, if I had my druthers, I would love to own one of those 'do it yourself' coin operated car washes. They rake in huge bucks, and all you really have to do is collect the money, pay the upkeep and hire a maintenance man or repair man once in a while. A buddy of mine in town who owns two of them is a millionare.
Any kind of a food place, however, is going to be more work. Even a fast food operation is going to require you to cook, clean, and do the office work.