I would go with the M60 Carbine which was used by the SEAL teams. It is similiar to the M60E3, those things were a bit lighter and they had the cool forward grip, hey a cool factor can be a plus
And it can do anything a regular 60 could do just a bit lighter, and the bipod is on the reframe not the barrel again adding to lightness.
The M240 is cool and all, but heavy, a good weapon to be left in the tripod for fixed positions, but humping it, fagetaboutit! <Unless the poll was what 7.62 MG would you like in a defensive position, and the minigun is a gattling gun so it don't count you smartys>
A close second although not 7.62 would be the MG 42
And the BAR is a weapon all its own, hey the Brits and Ozzies get Brens! But it is an "AUTOMATIC RIFLE!" Damned semantics.