Hi James – Two things I was told to look for when I bought mine were shell seats and Sync 3 entertainment system.
I do find the Sync 3 worth having but my wife moans about the seats (awkward getting in and out the car) personally I like them.
Try to find one with the Mountune MP375 pack fitted. This is the best addition I have put on mine but cost a grand so worthwhile trying to get an RS with it already on.