It's time for another love session with the M14.
The M14 is in my opinion the most satisfying gun to use in COD4. It's in the Assault Rifle class, but it's only in there because there's no Battle Rifle class. It uses the same ammo as most of the Sniper Rifles (M40, M21, and R700), so you know it's got some power behind it.
What really makes me love it is the one-shot kill. Shoot someone in the head or neck and most of the time it's insta-kill. There are a lot of stipulations to it (you have to use Stopping Power, it's only effective up to mid-long range and targets using Juggernaut negates it), but being able to whip out sniper kills with an assault rifle feels awesome. Just hearing the POW... TING! of the headshot gets me every time. And even without the headshot, with Stopping Power at any range for regular targets and up to mid-long range against Jugs, it's always a two-shot kill. I don't have a problem with people using Juggernaut, but I also have no problem at all with taking away most of its advantage.
I don't have much versatility with my setup, but the one I use (M14 w/ red dot, Deagle, 3xFrag/Stopping Power/Last Stand) is all I need to be effective with it. The M14 does really poor from the hip, but that's what I have my side arm for. I find myself using the M14 as I would a sniper rifle, going with my primary in medium to long range and using my sidearm in short.
While I still think the G3 is the best gun in the game, I've found that I use the M14 more efficiently ammowise, using less bullets per target, which means less reloading and feeling no obligation towards using Bandolier. I'm using the M14 almost full-time now over the G3, that's how much I love it. It also feels good using a weapon that not many other people use. I don't like to brag, but I've yet to see someone outdo me with the M14. I welcome any challengers though.