I didn't notice anyone else saying this so I will.  When I started I bought a 4 channel Airtronics suited my purposes just fine.  HOWEVER, no one else in my area flew Airtronics so I could not use the buddy box system for learning.  While park flyers may (or may not) be suitable for learning how to fly my experience has been that a bigger airplane and an instructor are invaluable.  That said, I suggest you might find a local club and see what they are using.  Then you can choose a low cost radio that will connect to one of their instructors' radios when you decide to go bigger.  DX6i is certainly a good choice.  So is Tactic.  JR and Futaba are typically more expensive.  And Airtronics (for some reason) seems to be lonely.  But then the radio I have had for 15 years now is a Hitec Prism 7X which talks to ALL 72MHz FM receivers and most transmitter buddy cords.