There's no real answer to that question, as it depends on your game style. I can be a beast using MP5 Silenced, can also beast it on AK47. I do well in L96 quickscoping, and I don't intend to showoff, just stating what I think about the "best gun" topics.
I picked up an HK21 with red dot site during a match, a gun/attachment I'd never dream of using as I prefer Iron sights and think the gun is utter toss, however I seems to do rather well with it. Point being, as said above, try messin about with lots of weps/attachments in CT and find something that works for you, could be a combo you wouldn't of dreamed of.
If that doesn't work you can always jump back on the band wagon with a 74u or your silenced galil.