Depends on your gamestyle, game mode and map.
On hijacked a smg is better.
On carrier an ar or a lmg can do better because of the longer lines of sights.
In BO my favorite weapon was the M16. Not the best weapon but I did good with it.
In my opinion..
Assault Rifles: M8A1, M27, Type 25, Scar H
Submachine Guns: MP7, Vector
Shotguns: KSG, R870MCS
Sniper Rifles: Ballista, DSR50
My 2 Best gun classes.
Primary: M27 w/quickdraw, fast mag, suppressor
Perk 1: Hardline
Perk 2 : Toughness
Perk 3: Dexterity, Engineer
no Tactical or lethal Grenades
Wildcards: Primary Gunfighter and Perk 3 Greed
My second class has the exact same this just instead of the M27 I use..
The Ballista w/ Ballistics CPU, Variable Zoom, and Dual Band Scope
In my opinion these classes work amazing with me while Im playing, Headquarters, CTF, TDM, and Hardpoint
Quickscopers Nuff said. If you can QS you can kill an smg in cQC and it pisses them off too lol. Ok but on a more serious note every gun is pretty balance there is no best gun. It all comes down to the person using it your tactics, and if you know the maps and your opponents also how to control your gun.
SMG- Peace Keeper since it is AR hybrid (I don't even have revolution and like it better than all others)
AR- AN94, very fast fire rate (on burst fire)+accurate+high damge
LMG- HAMR, it is easy to 'manually' burst fire it for fast shots + accurate+high damage
Sniper- DSR 50, Just my favorite of all
Shotgun- I don't use much, but R 870 MCS
Specials- Crossbow, I hate ballistic knifes+easy to stick people with crossbow
Pistols- Tac-45, very deadly and my highest K/D pistol
Launchers- I don't use, so the only one I think is in the game, RPG
I normally don't use a secondary weapon at all, though (just the tac with snipers)
These Things Are The Ultimate "Get The F*** Outta My Face" Weapons. (In My Opinion)
But Seriously, Some Maps Are So Clustered That Getting Kills With Them Ain't A Problem.