It is very difficult to select a single Tool album as the best, because all of them are tremendous.  Alongside Lateralus, I'd have to say this is my favorite, though.  Many people claim that Tool is the greatest band of all time, and I won't dispute that, but I don't believe that most people who say that have any clue as to why it is true.  As far as originality goes, Tool is very original, especially with their layered guitars and strange beats.  Maynard has an amazing voice, capable of soaring vocal solos and quiet whispers that sound great and blend well with the music.  On Aenima, though, it sounds as if they were trying to change their sound, and it worked out for the better.  Opiate and Undertow are also superb, but of all their songs, Eulogy strikes me as a masterpiece.  It is, of course, a eulogy to Jesus Christ, but it is hard to tell if it is sincere or a mockery of Christianity.  The idea is similar to "Judith" from A Perfect Circle, which is equally mystifying.  Anyway, I'm sure that anyone who is reading this has heard at least one Tool CD, but if you have not heard Aenima, get it today.