I have thought long and hard on this...This is really tough, being someone who loves/has loved fantasy for at least three quarters of my -of so- young life.

Loving the genre entails taking certain things for granted and certain things as "normal" in a completely UNnormal world/place. The idea of having a "favorite" seems almost counter intuitive since I should [and do] enjoy all elements of fantasy. Many call these "tropes" and somehow that is supposed to dismiss them as trivial or trite/"overdone."
I simply don't ascribe to that...in most things.
Favorite class [and I am shocked this hasn't had more responses]: Magic-user/Mage/Wizard/Sorcerer...whatever you want to call them. As we think of them now, "arcane spellcasters", someone who gets power not from the gods. This is FANTASY, folks. You don't like magic? Or argue about how magic "works." Find it "overpowered" or poorly defined...It's MAGIC! It is supposed to be mysterious. Even "low magic" is perfectly fine with me...psionics in a sci-fi or superhero or simply "non-magic but still psychic" world are all good...but don't tell me, in a "fantasy game/world" that I can't play someone who knows/does supernatural stuff.
What is King Arthur without Merlin? Or Morgan La Faye? Go Biblical, if you want! What is the pharoh's court/Moses story without the Pharoh's magicians? The Witch of Endor? What is Greek mythology [or literature] without Medea or Hecate or any of the numerous creatures with magical powers? What is [though it is kinda redundant to the Merlin example] what is the Lord of the Rings without Gandalf and Saruman?
If I'm playing fantasy, gods help you, there'd better be MAGIC!
Following that, gimme a druid...following that, I'll go cleric or psionicit/psychic in a heartbeat. If I'm playing a fantasy game, I'd better get some magic to use.
Least favorite: As indicated above, I don't really have one. I accpt the various archetypes and character concpts. I might not play them often, or in several cases "ever", but they do nnot make them somehow "Bad" character types for me as I've seen others play and enjoy them. Soo...good for them! Have I ever played a paladin? No. But I don't hold anything against them. Have i ever played a monk? Nope...and i concur with the difficulty in introducing them into a fantasy "pseudo-europoean fantasy world". But they're not a BAD kind of character. In an "Avatar: the Last Airbender" setting...or even the Star Wars/Jedi universe, not to mention the more traditional "Oriental Adventures/Eastern" style setting/game, monks would be/are awesome! Thinking on it, I don't believe I've ever played a Bard either, though ye olde Fighter/Magic-user had a character sheet or two. Straight Fighter, Barbarian, martial types in general, are simply not the carrot I'm looking for, though I certainly WANT them in the game...I'm not playing fantasy to simply hit things more/better than I can in the real world...though I know many like to do so.
None of this makes ANY of these my "least favorite." They simply aren't the characters I prefer to play.
I think the world, especially the online world (and worlds of fantasy, for that matter) can benefit a great deal from an outright rejection of binary thinking. We must stop thinking of any thing everywhere as "yes/no, most/least, best/worst, all/none." The computer age of all things being made up of "0's and 1's" makes this inherently difficult. But I think it would be good for all of us to
try.