Get the 6 channel radio. While you will not be using the other 2 channels with your trainer, by the time you get to your 3rd plane (2nd plane is USUALLY a low wing such as a 4 Star or Tiger II ) you will most likely be wanting flaps and/or retractable landing gear. If you buy the 4 channel now, you will need to buy a 2nd transmitter later when you want flaps and/or retracts.