AK-47: Silencer, Tuber, or just Straight normal. AK-47 rocks! Iron Sights are awesome and best overall in the AR section. Burst fire to snipe, and spamfire for close encounters.
G3: Silencer or Tube. Iron Sights on this gun allow greatly for either attachment. This can be paired greatly with Overkill Perk utilizing the G3 and M14 as they share ammo.
MP5: Range and Accuracy all the time. Silenced and deadly. I use this weapon when not wanting to just run around and spray like the P90.
Uzi: I prefer the Uzi or the P90. Yes strange. The uzi is insane for run and spray. You run, pop and spray and this gun with even silencer can mow down opponents FAST. Why I like it. DAMAGE.
M60: Uhm, it's an m60! It kills enemies thru walls in 1-2 hits on hardcore. Insane! Always, always, ALWAYS spam WALLS with LMG when approaching enemy area. This helps you as well as your team push foward.
Shotguns: Hugest advantage over all other guns is that the crosshairs on this weapon do not increase in size when you are moving at all. This gun is over the top for any type of close encounter. You can jump, and hip fire thru tons of enemies. The Insane amount of damage on even normal mode kills in one shot. Remember to Juggernaut this one.
Snipers: I like the Dragunov, I suck at sniping. The End. :-)