its all response speed. The fastest response would be the t-fhss SR receivers. but SR mode need to be turned on the radio and it requires a SR compatible servo and the servo need to be pugged in to the radio and sr mode also need to be turned on for the servo. When sr mode is turn on this is the fastest response speed but there is no telemetry. Only the futaba 7px and 4pm are compatible with T-FHSS-SR. Receivers are the r334sbs and r334sbs-e. The E receivers have an internal antenna and are only suppose to be used only with electric cars Where as the non E receivers can be used for both electric and nitro/gas cars. With SR mode turned off or when its being used with a servo without SR capabilities the receiver will function as a t-fhss receiver. the r334sbs and r334sbs-e can also be used on a radio that is not SR compatible like the futaba 4px and 4pv but the receivers will function as a t-fhss receive.

T-fhss is slower but has telemetry.

fasst is old and even slower

s-fhss is even slower

fhss is slowest

top end radio like the 7px is compatible with all the above type of signals and receivers. Some lower end radios are only compatible with certain signals/receivers.