In your case you have no choice, you have use a jack plug at the amp side. At the cab you have a choice, either jack or speakon. With regard to the amps power output it doesn't really matter what you use both are fine. Just don't use a guitar cable! These are for low level signals only. Speakon is a better and safer method of connection however (twist-lock, capable of higher currents, larger contact surface area, can't be confused with signal levels (line, instrument) commonly using jack plugs).