I chose the m14 due to its portability. Being able to carry and shoot is key. I would choose the venerable and infinitely sexy M2 for a mounted rig. MaDuece is a tough act to follow.
The question WAS, "...first full auto." My first choice was the HK MP5-N sear gun. That way you could buy a HK91 and HK93 and SP89 and use them as host weapons for the sear. Giving you 3 F/A cal's for the price of one.
I would love to have a MP5-PDW. I shot one in Vegas at a gun range and fell in love with it. Cant wait to get my hands on any other MP5 style weapon to shoot again
if I could only have one, I want the most versital I can get: M16 baby!
No ther platform will host more calibers. And if I could ever get a shrike upper, I can go belt fed like a SAW