Unless you are a huge AC/DC fan, i would definately go for the Metallica Pinball machine.
AC/DC is cool but i reckon the standup targets are too old-school and there are too many of them.
Actually, except for the pop-bumpers, and the ramps, the AC/DC feels a bit old fashioned for a new pinnie.
The bell has caused a fair bit of grief for owners and has been broken, replaced, broken again, repaired and broken again.

The Metallica pinnie is pretty sensational from the moment you step up to it.
It's got insane lighting, the drop-down targets are cool, the lights and artwork are colourful and interesting.
So much going on on the playfield, so much to look at, so much to shoot.
Playfield feels much wider than the AC/DC machine and you can get a lot of ball-speed up in places.
The Metallica ramps are pretty beastie, although i prefer plastic ramps as they dont scratch the balls and you can see through them to the playfield. Still, the Metallica metal ramps are pretty good and look hot.

Metallica is serious fun and there is so much on that playfield to shoot at. Lots of variety too.
Sometimes shooting a ball in the same location will have a different result, depeding on the targets you've hit.
I like the snake-head but it feels a little close to the flippers, (only negative i can think of for Metallica machine).

From the second you launch the ball, on Metallica, you're smilling, (guitar slide down the guitar neck as the ball launches ... absolutley brilliant!)
Then there's the music. "Sad but true!" OMG the music on this machine! AC/DC is very good all around but this Metallica pinnie is going to be a legend.
Metallica premium comes in 2 cases, the 'Monsters' and the 'Road Case'.
I love the backglass on the 'Monsters' and it definately matches the playfield better.
But the 'Road Case' has a more mature and band-like look about it.
Was thinking i'd buy the Road Case and swap the backglass for the Mosters backglass.
Best of both worlds, mate.

Unless you're Angus's best mate, id go for the Metallica pinball machine any day of the week.
It's heaps of fun, it's a great piece of artwork to have around the house and it pumps out speed-metal like ... well, just like Metallica

Id go for a Tron or a Star Trek over the AC/DC too, just to confuse the matter.
Metallica is a sic machine. It and the AC/DC mark the start of a new age of pinball, i reckon. Good stuff!