The following characters get my vote:
(1) Little Nicky (While I loathe the menage a trois-story revolving around Lucy, I actually think that Richard is a somewhat appealing and well-cast character. However, everything involving Little Nicky might as well not be in the final cut).
(2) James Hurley (I like the character, really, however James Marshall doesn't do it for me. I'd even rather have Luke Perry play the role. JM seems to have no charisma or facial expressions at all).
(3) Lana (She is gorgeous, but the stories surrounding her are dubious and below the general standard of Twin Peaks. She is a testament to a momentary lack of creativity during the second season, as is Nicky, and really should rather have been left out of the series altogether).
(4) Jean Renault (Now this one is a tough call. In some scenes he is brilliant, but there is just too much too much of the Renault-brothers. These brothers seem to stem from Frost's typical, run-of-the-mill police shows, and only Jacques Renault truly has the charsima - and Olkewicz the acting skills - to pull it off, all the way through).
(5) Sylvia Horne (Granted, she doesn't have much to work with, and her yelling "Ben!" in one of the first episodes does, in fact, clinch it for me. But - as opposed to Eileen Hayward and Betty Briggs who are also stereotypical housewives - Sylvia seems almost entirely irrelevant to the show. Betty has some funny over-the-top housewife features, such as the "We're here for you, Bobby"-scene, and Eileen some almost gripping moments. Sylvia is just filler, really).
Comments:
Evelyn is an interesting character, though the plots surrounding her and James are, at best, noir-clichés. But the somewhat dubious quality of these scenes have more to do with James than with Evelyn, in my view.
Donna is a gem of a character. I absolutely adore her. She is annoying, but only insofar as it serves a purpose for the plot. LFB does an excellent job, and Donna is deservedly one of the most important mainstay-characters of Twin Peaks. The series wouldn't be the same without her.
Sarah Palmer is wonderful. I love her shrieking and insane eyes. She is not only an important character and an excellent actress, she is even imperative to the surreal and uncanny tone of Twin Peaks. She may be tough to take and hard on the eardrums, but she is no less than amazing. I'd go as far as to say that she is almost otherworldly.
Annie is a bit on the boring side, but she is well-played, and the 'love story' surrounding her and Agent Cooper is intriguing and believable.
Nadine is a wonderful character during the first season. I love her and her "silent draperunners". However, many of the different plot threads involving her during the second season fall short of being poignant, comic or even surreal. The adrenaline-pumped Incredible-Hulk-type sub-plot is embarrasing and laughable, and should in my view have been sacrifised as well in the editing process.