I enjoyed the morbid pessimism of the fifth book. But yeah, most people are talking about the first two --- which are really an adaptation of a radio show, and are only two books instead of one because Adams couldn't meet his deadline --- and maybe the third, which is more like the last two in that it attempts a plot (which is a bit tricky when you have Infinite Improbability Drives around) instead of being a bunch of absurd jokes and situations strung together, but still has some of the best jokes in the series nonetheless.