Welcome to FlyerTalk!
Before knowing whether Priority Pass or a RCC membership is the best option, it would be helpful to know your flying habits and which airports you fly to the most.
Even though your Priority Pass membership would be discounted, it doesn't help that much if the lounges are not in the airports (or even in the correct terminals of the airports) that you use the most.
If you fly United the most, the RCC membership may be the best since the lounges will also be in United terminals. If you fly other airlines frequently, see if Priority Pass has lounges in the terminals of the airports you use the most.
Good luck,
Bruin