All the watch ones are amazing and there also a bit longer which is good. I like the witches but not as much as the watch. But my one favorite would have to be Unseen Academicals, which I'm now reading for the third tome since I was given it for Christmas.
I'm re-reading UA at the moment, and getting more out of it. When there's a new TP book out, I tend to devour it at one sitting and then leave it for a while before I go back and take my time over reading it again (and again, and again.)
I haven´t read all the books so I can´t be truly fair in this questions and I also tend to think that the book I´m reading at the moment is the best one (that means that I´ve had 6 favourite books during the last 2 weeks ).
But Thief of Time, Hogfather, Night Watch, Going Postal and Witches Abroad are at the top of the list....I think
Ooh, really tough question! I think the City Watch books are my favourite over all, but Wee Free Men stands out as the one which made me laugh so much I had tears running down my face.
Favourite is probably too strong a word. I'll always have a soft spot for Mort, because that was the first Pratchett I ever read.
But having being in bands, Soul Music really speaks to me. Sir T must have been in bands and played crappy gigs on the toilet circuit to have written it
Currently re-reading Guards Guards, and loving it all over again, but high in the rankings (in no particular order) would be Going Postal, Making Money, Pyramids, Soul Music and Moving Pictures (my current handbag book for use on trains!!).