The voltage on the screen grids of the power valves used in the power stage of virtually all guitar amps is almost exclusively responsible for the acceleration of electrons from the cathode, so has a significant influence on the current flowing through a valve.
Any ripple on the screen grid will cause hum on the output, so virtually all amps employ extra filtering of the HT for the screen supply of the power valves (the exception being "ultralinear" amps).
This can be done with an RC filter (resistor then capacitor), or an LC filter (inductor aka choke and then capacitor).
The effectiveness of the filtering is determined by the resistor, capacitor and choke values used, where larger values give more filtering, ie reduce ripple.
Increasing capacitor and choke values increases cost.
Increasing resistor values is cost neutral, however resistors drop voltage in proportion to the current through them (Ohms' law), so increasing the R in an RC filter will cause a reduction in the screen voltage (especially under load), and thus a reduction in power.
When an amp is driven into clipping (does that sound familiar?), then the screen current rises dramatically, and and RC filter will drop more voltage causing the screen supply to sag giving a "compression" effect. This may or may not be desireable depending on the users.
The situation with an LC filter is slightly more complicated. When more current is draw through the screens, the energy stored in the choke will try to maintain the screen voltage, thus preventing the screen supply sagging. However the choke can't hold the screen supply up indefinitely and under sustained overload the screen supply will start to sag. Thus an LC filter will have a slightly different dynamic than an RC filter under sustained overdrive.
As a sweeping generalization, an LC filter gives better ripple rejection and higher power but is more expensive, whereas an RC filter is cheaper and causes more compression on overdrive.
A choke is usually favoured in higher powered amps, as an RC filter wastes power (which presumably is NOT the point of having a high powered amp).
Neither is better, and great amps have been built using both RC and LC filters.
