Simple Question, Not so simple Answer.

[XC700116]

One I'd actually shoot, an AI PSR Kit with an S&B 5-25 PMII on top and TBAC suppressor, And about a 4 other barrels that I'd add to the mix in different calibers. Or a JP LR-07 with a custom chambering in 6X47 Lapua, topped with an S&B Super Short.

for a pure giggle stick, M2 or minigun.

and Collector/Value gun something along the lines of what TimK said, not sure on that, then I'd probably sell it, and buy most everything listed above and go have a ton of fun with it.