I find the CQB sort of annoying. I have one, and I... don't use it all the time. Sometimes I'll buy random GP weapons because I feel like change. To me, the GP M416 feels way smoother and easier to use, while the CQB... it's just so bulky and awkward. I got my first unbelievable with the CQB version, but that was pure luck, so nevermind. I think that the UMP is really annoying, though, what with the recoil. I've gotten so used to the amazing lack of all recoil that the M416 has that it's hard to use any other gun, although sometimes I need a break from the monotony.
Basically, trash your UMP and get an M416. Don't get the CQB version, although that's just my opinion. And if you're too low of a rank to get it, get a FAMAS. FAMAS's are weird, but... you get used to them. They have amazingly low recoil.
...I totally rambled, but rambling is the sign of a great mind. So, bow down. Worship my opinion.
Unless you don't like it.
...and in that case, go ahead and... move on to the next comment.