I have been playing MW3 since just before it came out (thanks to couriers for early delivery). One thing stood out. Range versatility. Sometimes I use a sniper, and screw myself over for corners, and frankly and MP9 is not going to touch the PP90M1. It won't even tickle it.
However, I came to realise that my classes were relying on one weapon, and a back-up, so I started playing around. I finally hit on a wonder-class.
Primary: ACR 6.8 Assault Rifle
Attachments: Silencer, Grenade Launcher. Yeah, call me a n00b, I don't really care, it works and that's all that matters to ME.
Camo: I either use Digital Urban or Multicam.
Second Primary: Barrett .50 Cal Sniper Rifle
Proficiency: Impact [I use this when somebodies gun is poking out of a window, I aim through the wall where I guess their shoulders will be, and fire, usually get a kill or a paint.]
Attachments: Extended Mags
Camo: Digital Urban or Multicam
Lethal: Bouncing Betty
Tactical: Concussion Grenades
1st Perk: Recon Pro [If my GL doesn't finish them off, I can track them down, also useful for spotting targets for my team, and if my sniper doesn't kill them; especially if I wallbang, I can find them].
2nd Perk: Overkill Pro
3rd Perk: Dead Silence or Sitrep [Whichever I pick, the other goes as a killstreak].
2 kills: Assassin
4 kills: Sitrep or Dead Silence [Whichever I didn't pick].
6 kills: Sleight of Hand
If I start to run low on ammo, I go really stealthy, and try and either pick up a silenced weapon or use my remaining rounds to secure myself the 2 kills I need for All Perks, to get Scavenger, though it rarely comes to that.
I rarely sprint with this class, except to get to cover. I use this class for Search and Destroy, or Team Deathmatch. Free-For-All is too fast paced to be using a sniper, and the Grenade Launcher takes to long to pull out, fire, and put away. It takes even longer if I need to fire another round off.
I walk around corners with my aim already up, as another poster has said, my .0 seconds to pull my sights up beat his .2 seconds even with Quickdraw, it's about .35 seconds without QD.
The ACR is a stable weapon with moderate damage, accurate up to long ranges, though a sniper will prevail in most cases. It is capable at close range, but succeeds most at mid range. It has a slight upward pull that makes it efficient at mid range if you aim for centre mass, as recoil wilk walk the rounds to the head, at long range 3-7 round bursts are effective. No red dot sight is required, though they can make the weapon even more effective if you decide to swap out the GL for such a sight. On some maps the ACOG sight is a better choice, but to control the recoil it seems to give the weapon a silencer helps, as does burst firing. The thermal sight is also a good option, and goes well with extended mags and smoke. Using a shotgun is an idea, but due to the rarity of 1SK's (1 shot kills) it is a risk.
The Barrett is a good weapon with a decent fire rate. The recoil is terrible so the first round must do the job as double tapping is not going to work. The damage is one of the highest out of the Semi-Auto sniper rifles. The accuracy is high, and quickscoping seems easier with this weapon. This weapon works well with the ACOG scope and a silencer, though it definately comes second to other semi-auto's. The M14 is obviously also a better contender as it supports Holographic and Red Dot sights.
The bouncing betty is a bounding landmine with a good radius (about 2 metres), but it has a major flaw. It is useless if the enemy goes prone, and requires Line of Sight to trigger, to it can often be misplaced. The C4 will do a similar job as the Bouncing Betty, but requires human triggering (whether by gunfire or clacker). A claymore is also a good option, but the lasers give it away, it is an easy target in shape, throwing range is very limited and it is directional to 180o give or take. It can easily by avoided, and can even by destroyed by knife, with no consequence to the knifer.
Concussion grenades are effective with Recon as their effect range is quite large (second to EMP), they slow down enemies (which painted, are easy to take down), and they don't explode in mid air.
Thankyou for reading my guide to the perfect mid to long range class, and alternatives.
I am Darknight399, I hope you follow me and enjoy playing the game.