Ok serious best pvpers on Siege in my time in no particular order:-
Rumpy - Decent dueler, awesome field fighter back during the real 24 hour faction sits pulled of some crazy wins against insane odds.
Shakaja - King of the ******** overpowered template and could basically play ANY combination of skills well.
Arden - Best field fighter bar none, could heal himself while dumping a target and healing me with a wand all that same time. You don't win 2 v 12 fights with a bad teammate
Forsaken/Meph - Two best pure mage duelers i have ever seen play, at least with Meph i know he travelled around prodo shards for a time dueling for gold.
Prymal/Will X - Two best dexxers i have ever seen, Will X was good on Will X but on Scourge was an absolute beast, probably the first real theory crafter i have seen in U.O. Prymal was probably the best pure dexxer dueler on Siege for a long time, only just losing Siege's biggest ever dueling tourney to Calamity's crazy op necro template and cutlass
Lilly (Maybe the wrong name) - First really prominant ninja/stealth/tamer on Siege and easily the best there has ever been and this was back when you could still use monster ignore against player pets. Hardly ever risked fighting in glow without 40 lifeforce purely because of him. Yes it was overpowered bs but when you do it first and do it right you get credit for it
Feyre - Probably killed more people than most real pvpers even though he was a thief, probably guardwhacked ten times more people that that. One of the smartest players Siege has ever had when it comes to "clever use of game mechanics"
Lother/Dalton - Only ever had one proper 2v2 fight against these two and they were a good team but LoD was virtually done when i really started pvping so i can only really go on what i know first hand.
Lots of other very good players i have been guilded with or fought against but those are the ones i have really seen stand out back when Siege was populated not what it is now.