I prefer LiveJournal because it allows posts and replies to be long enough for nuance, and for discussions to be threaded so each tangent can go on a separate branch; it facilitates interesting discussion. Twitter, at its best, encourages eloquent, succinct writing with its 140 character limit; I think most of the people I follow on Twitter make their living as wordsmiths of one sort or another. (Sturgeon’s Law applies, of course.) Facebook doesn’t do anything to facilitate either one; I gateway my Twitter and LJ to it so people who know me on Facebook can see what I’m posting, but I rarely put anything original on Facebook itself.