Presumably your RV will have a square tube receiver, so either you use a direct mount (has a square "stinger" that fits in the tube) or a coupler, which would require a ball mount inserted into the receiver. You could insert a pintle hook instead of a ball mount, but that is of vale only if you have a reason to need a pintle (e.g. to tow farm equipment, or do very frequent disconnects, etc).
There is little reason to choose a ball mount either, unless you have reasons for having a ball available for other towing. However, the less expensive A-frame tow bars all use a ball mount. You generally don't get the ball & socket type until you get into the upper tier tow bars designed for maximum convenience.
Personally, I like the convenience of the high end ball & socket tow bars that slip directly into the receiver. They are the easiest to hitch/unhitch, especially on uneven ground.
