its not nooby, but the worst attatchment has to be ACOG.....
ACOG can be alright on some guns, like the M4A1 and ACR, but I'd still pick other attachments over it.
M203 is the noobiest attachment but only if you use it like a fag. There's nothing wrong with using a Grenade Launcher in moderation, for example clearing a room or trying to keep enemies off an objective. Saying that, I still think they should be taken out the game, but if they're in there then use them properly.