This is can be controversial. I have both. I like both simulators. The answer is based on your intended use. RFX can be more gamelike when used in FPV mode. Both simulators have VR capability. I like using the simulator to practice flying at the local field. My choice for that is RF9. If you want wireless, you only have one choice. I believe that you are limited to 8 channels over the USB devices. That means that you need a wireless keyboard and mouse. I can't give you an answer, just some of the considerations.
Good luck. RF9 is really not that expensive and the InterlinkDX is great.