I'll start out by saying that all of them are good, and you can't go wrong with any of them.

That said, the next order of business is, regardless of which one you choose, you'll need an instructor. Without proper instruction, whichever one you choose will become a pile of splinters within a few seconds of takeoff.

Now, for the specifics.

The Nexstar has a feature than most people feel needs to be removed right from the get-go, and that is it's built-in autopilot. I have not tried it, but many people here who's opinions I respect say to disable it. The RTF version comes with an excellent engine

The Alpha and Superstar are about equal. Everything comes with them, and they are RTF in minutes. But for the extra 10 bucks, the Alpha has a MUCH better engine.

The Mustang PTS does not have the self-righting characteristics of a basic trainer, however if you ARE GOING TO HAVE A GOOD INSTRUCTOR, it gives the most bang for the buck since it can grow with you as your skills improve.