I am still around from time to time. While I can't really comment too much on the current crop I can mention some well remembered baddies.
Thief- Best all around thief I will give to myself hands down every time. However right now and for a while it has been Narissa. Overall just pure fighting Xandamere was nasty.
Sorceror: I would love to say Huzow all time because he scared so many people as a sorceror however when he was scaring everyone I still beat him easily and quick in our friendly challenges so I would have to say Panaideos all time for me.
Knight- As a young thief Bedivere whooped me and had all my items in no time after I tried robbing someone.
Mage- All time criamulus, different time, different skills but scarry! Modern probably Fistadantilus.
Ranger- all time toss up between Wotan and Ender. Both were just great with ranger skills.
Animist- All time Dhonuill. Good times.
Seer- for me was Cordon, I just could never pin him down.
Bards- Culinane, I hear Max does some good things with the skill set these days but Culinane intimidated alot of Thakria in his day as Prince of Mercinae though most will deny it.
Loremaster- From enemies it was Allanon. He terrorized alot of us growing up. However from skill to me it is a toss up between Zenichiro and Kodiak. I would want either or both on my side in pretty much any group competition.
I know I mentioned thief however I would be remiss if I didn't give honorable mention to Sturge, who I think falls just short of Xandamere in fighting and Calagan as one of the all time amusing great schemers of the guild!
Written by my hand on the 18th of Leaflost, in the year 1197.