Well,we all agree that Modern Warfare 2 is a great game, right?  Campaign is easy enough, but when you get to Online, it's a whole different story.  I remember the first time when I played that my final score was 0-15.  That was terrible though I did get the accolade participant.  I got better eventually, but then realized that others might have the same problems as me.  Hope this helps!

SCAR-H: This is like the M4A1 on steroids.  A heavy assault rifle with a slowish rate of fire.  However, it makes up for damage.  This gun is good with the attachments silencer, red dot sight, and FMJ for extra damage.

ACR: Another great heavy assault rifle.  This gun has more strengths then the SCAR-H, like mobility, higher rate of fire, and better accuracy.  However, this gun has less damage then the SCAR-H.  Good attachments: Red Dot Sight, silencer, and grenade launcher.

AK-47: One of the world's first automatic modern assault rifle just went rambo.  This is a all powerful gun good in every category. Need I say more? Good attachments, everything.  Wonderful gun.  It's like death in a can.