Favourite character is a toughie. There are quite a few who would make it onto my shortlist. I think overall though, I'd have to go for Theoden. I was so terrified that they were going to leave the Ride of the Rohirrim out of the film and when they came to it and then Bernard Hill delivered it as beautifully as he did it was one of the highlights of the trilogy. I also felt that Hill really captured that recovery from his ensnarement by Saruman well- in particular the scene where he says: 'It is a cruel fate that any parent should live to see their child's funeral.' (para.). I also felt that he encapsulated that sense of satisfied achievement in his death speech to Eowyn particularly well, as though he felt he had finally righted the wrongs and died for a noble cause.
Now, my worst character. I'm afraid this is a not-too-shortlist.

I'm going to have to just come out and say that it's Elrond, though. There are just too many things which I feel aren't right about him. Firstly, and I'm going to get this out of the way and not mention it any further, I don't think he's beautiful enough to be an elf. Secondly, there's the way he plays the father. Sure, there are the times when he looks after Arwen in TTT and the look as he nods for her to approach Aragorn in Minas Tirith in ROTK, but overall I just found him a sly, manipulative, low-down double-crossin' varmit! Ahem. No, but seriously, I found him to be very manipulative. And then finally there was the snobbishness that I just didn't get a sense of in the books. In the films he seems dismissive of Frodo's chances as well as those of man, and overconfident in his own gift of foresight. I really thought that missed the mark for Elrond, and it didn't impress me at all.
Ok then, there you are... now let me have it!