Hi Woketman,
If all you want to do is trap RF ferrite rings or beads will do the trick. If you want to keep RF away from your servo amp to prevent TX's in close proximity to "break in", place them close to the servo. If you want to break the groundplane effect of the wiring system, place them close to the RX. Do both if you want, it can do no harm.
However most perceived "RF" problems are because the servo pulse has to travel on the same ground return path (negative lead) than the servo power. This induces noise to the servo amp output.
The ways to get rid of it is:

1> use an opto isolator at the SERVO end driven by SEPERATE signal and ground return wires, twisted if possible. This eliminates all common mode noise as well as power supply noise. NOTE: Some opto sets sold actually use the same ground return again when using opto isolation. Absolutely pointless. The slight slew rate limiting effect of the isolator is then what actually reduces the noise.

2> use an optoisolator with battery next to servo, same effect as above.

3> put a 10 nano ceramic cap accross the signal and ground wire (reduces noise and limits signal slewrate a bit) as well as a high value low esr cap accross positive and neg wire at the servo end (1000 uF or more, reduces current peaks in the long lead) Most simple and harmless solution. Requires good soldering technique for reliability.

This is all pretty straight forward signal transmission line techniques.

Cheers
Andre