There is esentially no difference, assuming the 50A outlet is wired properly, i.e. 50A/220V. However, each of the two hot legs of the 50A circuit has a 50A breaker, whereas the 30A circuit will have a 30A breaker. Your Rv's power panel, of course, has a 30A breaker in either case. The subtle difference is that you don't have 30A breaker protection on the connection between the site power pole and your main breaker. Not something I would lose sleep over.
It's conceivable that in any given situation there will be a difference in the actual power available on one outlet or the other, due to the vagaries of park wiring. No way to predict that, but if I were having low voltage problems on one I would switch to the other to see if it might make a difference.