Serial Bus (SBUS)
If your radio supports SBUS trainer input, this is the recommended choice. SBUS is digital fast and supports 16 channels. The only reason I wouldn't use SBUS is if you have a long cable length or electrically noisy environments. A single missed bit will cause a whole 16ch update to be lost. Although PPM is slower it is more resilient to noise.
SBUS trainer isn't supported on many radios. But if you have an OpenTX radio you might be in luck. Below are two known working.