I'd say the MK48, but the LSAT is more well rounded. The MK48 is the closest thing to what a stereotypical LMG has: Slower RoF,high damage/range, fairly accurate, molasses reload. Definitely the gun to use if target finders are your thing.
LSAT with the HAMR/MK48 at second depending on your playstyle. --- "Accepted disgrace in the place of honor... Hate in the place of love... And still he died with a smile on his face, fooling you to the very end."