It is well-known that the Pythons themselves believe "Life of Brian" is their best movie.  In terms of production value, it probably is, but it's not nearly as funny as "Monty Python and the Holy Grail."  Made on a shoestring budget and played absolutely straight by the troupe, it is hilarious and intellegent at the same time, as well as being charmingly rustic (due to the low budget).