Have both, but new to AmpliTube 3 (for $99). So far...and it has only been a few days, but I'm not liking AmpliTube that much. Not just the sound, but the way they setup the base version... some patches you don't have the components for. Not intuitive.
All the "add-ons" are a SCAM IMO. If I want to just toggle and look for sounds that I like and inspire me, GR5 wins. Don't care how "cool" it may look and how many components I can buy. I'd rather pay a larger amount and have IT ALL at my disposal when I'm up @ 3am trying to find the right sound.
My verdict is not final, but so far that $99 isn't well spent.