My favorite is easily the guy who camps ducts with panz and only plays the axis side. When losing he always blames others, but I honestly have no clue who the guy is because he always has a different name. You always know it's him though.
http://yawn.be/findPlayer.yawn?nick=&pbGuid=25a3782b&gamecode=RTCWMy other favorite would be w@ste. The guy is hilarious.
Least favorite would be Sikwitit and his flamethrower TK's.
After that would be the constant accusers of hacking.