Since I'm among the relatively 'new and developing' fighters of the land I thought I'd just post my thoughts for recent fighters.
Loremaster- Taking gems into consideration, Kodiak truly is an unstoppable fighter, nigh impossible to kill and all around brutal. Gems aside however I think I have to agree with Killinan that fighting purely as a loremaster, not a bear or other form of gemholder, Meerkat takes the crown.
Knight - Lots of knights around with various types of style, and having fought pretty much all of you *grin*, I would say that Kureishi takes this one for me, difficult to kill and with a very potent style of offense.
Thief - Call it nepotism but once again I think I have to say Narissa, wonderful at staying alive and always displays creativity using trapping particularly effectively. Kudos to Foxedup, however for being the most difficult person to pindown and kill I've ever met!
Seer - Tough to call this between Esprii and Cordon, both excellent and creative fighters. I would say Cordon over Esprii in terms of being damned IMPOSSIBLE to track down and trap, though I think Esprii gets an honourable mention for sheer relentlessness, as well as being the best bash-ruiner I've ever seen.
Bard - I give this without a doubt to Maximillian, having mastered a difficult skillset to deadly effect, and generally being able to cause mayhem with it!
Ranger - No question here again, Elmak takes this one, uncatchable and deadly, a very skilled and creative ranger.
Sorcerer - I'm disinclined to say Saroman here as I think he does rely a bit too much on the initial shock and fear-factor of the jump, rather than showing a strong creative strategy, thus this for me has to go to Eldereth, showing unparalled creativity and a very strong potential for taking damage while still pushing a potent attack.
Written by my hand on the 25th of Leaflost, in the year 1197.