If you are a guitar enthusiast, TuxGuitar could use some features to help it catch up to where guitar pro was at version 4. Not sure how feasible that is.
Arobas has essentially rendered old .gp# tabs obsolete as their playback on new versions of GP is broken AF. Vibrato is weird, markers are bugged, its a bummer. I've been on GP5 since it was released and I refuse to update regardless of how "good" the new versions are.