That's quite easy for me.
1) Shaytan (not sure about the exact spelling). That guy is ridiculously good with a (great) lance on his courser. He should talk less about using his 'hax' as he calls it. Don't be afraid that we will call you a cheater
Ok, just found out that it's El-Diablito on these boards
2) Fredelios. Also good with a lance, but very decent with melee weapons as well.
There are two other guys who play very well, can't remember their nicks though. I think that those 4 combined make up 50% of my deaths ingame
edit: the third one is Rallix (also not sure about spelling).