No such thing as a "one pin collection"!
Who is the audience? Just for you? A family with kids? the DMD games are starting to feel more and more dated lately and if I can only have ONE pin, its NOT going to be a DMD game, it would be Iron Maiden. If I have a family in the mix, I would go for a Guardians of the Galaxy - they can be had for a fantastic price for a pro (sub 5k) and offer a ton of technology and a pretty solid layout. The new code has gone a LONG way. The LCD technology is leaps and bounds better and more attractive, especially for newcomers and kids. I love Metallica as much as the next guy and owned a premium for awhile but I wouldn't go back that direction - especially not as a single pin "collection"