If your PTS has a radio, use it. Pull the receiver out and put it in your trainer. This'll help to keep you from starting down a nasty little path of feeling locked-in to one radio system or another. It gives you some time to start learning how to fly, while at the same time learning more about both radios and where you see yourself going in the hobby. You'll find out about your local conditions - - is 2.4ghz necessary or recommended? Are there certain 72mhz channels to avoid?

I think that the last thing you want to do is to saddle yourself with a collection of radio gear that doesn't really meet your needs. If your PTS came with a full setup, use it. You'll learn so much in your first month or two of flying. That will give you a much better perspective from which to make radio choices.