Probably 3 b cuz it has Slow Ride,I Wanna Rock And Roll All Night,Welcome to the Jungle,and the legendary Through the fire and flames(or whatever it is called,i get confused with that one easyly).
gameplay- gh3 because of hammer on and pull offs and the tapping thing is just stupid (or is tapping gh4?)
songs that come with it- gh2 they kick butt
song that you buy- gh3 because that's where you buy all of the songs now go figure they already have metallica's lastest album on there which came out yesterday death magnet
so i guess gh3 had a run for its money and closely in 3rd is gh2