FOTR is the best edited/most concise of the three, definitely. But I still think TTT and ROTK are great as well. IMO the storylines in those movies aren't nearly as compelling as in FOTR, where you're mainly just following the fellowship. In the second film you have to deal with Frodo/Sam wandering around, Aragorn/Legolas/Gimli hunting for hobbits and the annoying Merry/Pippin story; plus the movie has the most annoying scene imo, ie the part where Aragorn "dies."

ROTK is more focused imo, at least until the very end; the multiple endings don't piss me off but they definitely could have been handled better.