The answer to this really depends on your RV and how many appliances you have. For a smaller RV with not many appliances, 30 amp is fine. However as more RVs are becoming better equipped, it’s becoming more common for them to be 50 amps. A 30 amp service is enough to run an AC unit, refrigerator, and electric water heater at the same time.  If you need more power to run more appliances then it’s a good idea to get a backup generator, this will give you an extra power boost for when you're using more appliances like cooking.