Out of that list either noob-tubers or mlc'ers (knifers). At one time would have been akimbo shotguns but they've generally been nerfed enough that they're "balanced"*
What is starting to annoy me is people complaining that IW don't listen to the community, Treyarch are so much better etc and so on, mainly as a result of some of the broken aspects having been removed in Black Ops. These people obviously have a relatively short-term memory as they have managed to forget that they removed the javelin glitch, the extra speed boost from care packages and nerfed the akimbo'd 1887's (twice) and all of which were done a damn sight faster than Treyarch fixed the broken maps in WaW.
Also a possible reason much hasn't been further nerfed recently may have a little something to do with the substantial numbers of staff who left IW following the whole Activision subsidies/salaries "issues". (Note both screwed up in letting flaws get through "testing stages" assuming any was carried out in the first place, just stop saying one is crap and the other is amazing, they're both crap)
Also those who say the perks system is "flawed" providing those who are just starting a handicap against those who have leveled up and unlocked other perks. Its such a heap of rubbish, the best perks are generally available from the very start or close to it, only exception being cold blooded which is about level 27 odd and protects from killstreaks. Apart from that I would imagine the perks most people use stay the same from the low levels to the top.
Sorry for the rant but had to put it down somewhere.
*Someone once accurately described MW2 (imo at least) as having balanced weapons, but they were all just too powerful.