The SCAR-H with a standard barrel (what's in KF) has a weight of 3.58kg. About equal to the M16A2, which is what the US army uses as their main weapon.
The M14 weighs about 5.1kg, i'd add a bit more given that's the proper one, not the hunting stock version in KF.
The SCAR-H has controllable auto-fire, and the M14 would be a sky-shooter on FA.
And in KF... the AimPoint M4S red dot scope with a 3MOA dot is far easier to aim than the M14's laser or sights over long distances, and indeed in close quarters as well.
The L6 SCAR-H has 5 more rounds than the M14EBR, which potentially means 5 more kills per reload. This is a big bonus to the SCAR-H.
The SCAR-H can also be carried in conjunction with a Romanian Draco AK47 variant and either an MP7M or katana; or pipe bombs and a machete.
The M14 is not so versatile... anymore.
The two weapons are of similar price, and can both be acquired after wave 1 by someone either playing extremely well, or by a killwhore.
All-round the SCAR-H wins in my opinion, however i'd prefer the M14EBR for anything that has motorised weapons for forearms
