I've gotten 2400+ in rbgs (dot cleave is hard) and 2.2k+ in arenas but I suck at 19s lul.
On topic: I'd say the best 19 is someone who is very skilled at any class they play on. Ex: Stubs/Yowza (I think he plays a lot of classes)
Something I'm interested in, my mage (fire) is on horde tich. peaked at like 2420 or so last season but finished low 2300's (carry groups :/ whatever though)
However, my computer broke recently (typing on a bad laptop atm) and I haven't been able to log on since a couple days before MoP release...
I achieved grand marshal on my fire mage this season in RBG's (lol dot cleave), and it wasn't very difficult as long as people knew the general concept of spreading damage (keep in mind I did get 2200+ in the other 2 seasons) and I can tell you that the 15-19 bracket does indeed take more skill...