I always go to see these on Christmas day, a "tradition" since the first film. I am currently watching "Fellowship-Extended Ed" on my 51" widescreen HDTV to be followed by "The Two T's-Extended Ed" just to get me in the mood.
Two co-workers went to the "marathon" and loved it (ROTK). One said it was the best, the other thought Fellowship was the best. Interesting to contemplate what I will think is the best. I guess one should view all films as a whole. Of the two I have seen, Fellowship has the lead.