I'm not really sure Lucien counts as a final boss. He's more of an interactive ending. I consider the Spire Shard to be Fable 2's final boss. Not much better, admittedly, but at least it puts up a fight.
As for my favorite, Yami from Okami, definitely. Its a nice, long fight thats bookended and punctuated by a couple very good cutscenes. Also, the boss theme is one of the best, if not the best song in the game. Plus the fight just has a great feel. Its long, tricky without being overly difficult, and acts like a big final test for the game, making you use everything you've learned throughout the game as you go. Its very cool. Plus, Yami just looks damn cool.
Worst....well, there have been a lot of genuinely BAD fights, but for most disappointing I'm gonna go with the Human Reaper from ME2. Its short, its boring. Its a fairly CLIMATIC fight, but it comes right after one of the most intense sections of the game and just kills all the pacing. Plus, the Reaper looks stupid >___>. Like a giant Terminator.