This is very subjective. Everyone has their opinion about the pro vs premium...some say they prefer one over the other due to the pro being faster (has standup targets for ac/dc and t.n.t) while others will comment on the lower play field on the premium and how bad it is. The fact is that the premium has more active parts to it. The bell swings, drop targets, molded train, dancing band, TNT detonator moves, lighting is great, powder coated red trim with lollypop rails, lower play field etc. I believe that this was one of sterns biggest pro/premium jump. And BTW the lower play field isn't that bad like many people say.... it's only activated when you play a song with "hell" in the title. Even then it only comes on when certain shots are hit. I played for a good hour once and it never came on. And when it does it's not that bad. You can adjust the timer for how long it is activated.
Metallica and Aerosmith pro/premium on the other hand aren't that significantly different from each other. Again others may argue this because of personal preference.
My advice is to try and play each game to truly get a feel of what game best suits you. I have played all of these games before and I would choose Metallica pro out of the bunch. AC/DC would be second and Aerosmith behind it. Metallica is one of the best pros stern made...game is risky, rules are great, and working towards CIU is very challenging and rewarding. Good luck with your decision. Either way it's a win because if you tire of the game you will be able to sell it as these games are popular.