This is a can't lose situation...all great games. Aerosmith's new update sounds awesome, it's fun to shoot and great looking. AC/DC has that sweet Steve Ritchie flow and a nice deep ruleset. But Metallica...that MIGHT be the best game ever made. Layout, rules, art, humor, music, custom speech from the band, inline drops, etc, etc. Total package game all around. That doesn't take anything away from the other two though!
I personally like Metallica best, but I know there are many people who think AC/DC is one of the best ever (I like it a lot, but it's not quite on my must have list...yet). Aerosmith is a bit of a dark horse that no one expected to be as good as it is, and the new code pushes that even further.
I think you would be happy with any of them. Heck all three would make for an awesome collection that would compliment each other well. In your shoes, I would make sure you play all three, and if that doesn't help narrow it down, go with the one whos music you like most! You can't go wrong here!