I own GnR and an acdc premium. Even though they are both music pins, they are totally different games. I like the music set to the shots and game programming on GnR, but also like how you can select the songs on ac/dc. With leds, the multiball light show is just as awesome on GnR as ac/dc. You have the cannon on ac/dc and the randomness of the magnets on GnR. Sure GnR is another 6 ball game from DE, but the music and programming made it their best effort IMO.
As jalpert said, neither will be leaving anytime soon if at all!