It's obligatory question, let us know why you like you favourite work of the Grand Sproutmaster.
I'll start:
It's Witches of Chiswick, 'cause I'm in it.
My fave is a toss up between two, Armaggedon: the Musical because it was the first I read and The Garden of Unearthly Delights, Just because..
I'm going to settle for The Garden of Unearthly Delights as I have re-read it at least a half dozen times and it still never fails to both amuse and excite me.Gotta be Armaggedon: the Musical, it was my first. I read it after a review in the Red Dwarf Smegazine. Not looked back since
Just have fun
The Antipope - First book written, where it all started and also who can forget Cowboy Night!
Who can forget what? 
Because it's the first RR wrote and the first I read (on Pratchett's recommendation).
And Apocalypso - because it's good and because I was at the UnConvention where RR got all the ideas from. Despite the fact that he blows up Croydon in it.
Witches of Chiwick - I'm one of the 100 people thanked at the start but it's not my absolute fave. Da Da De Da Da - I'm in it... but...
Actually I think that the next one is my favourite because apparently I'm in it and I'm not called a cunt.
I haven't read them all yet, but I loved the Witches of Chiswick. I need to re-read it because I got totally confused over the different time travel versions of the main characters. I loved the description of the Fairy Feller's Master Stroke which I'd just read about in one of Pratchet's Wee free men books, so now I want to see it myself. The Terminator rip of and the Steam Punkiness were great fun.
Doctor When and I listened to it as a talking book when on a long drive, then Doctor When took it home to finish it off. I kept asking 'what's happening?', but he said he didn't want to spoil it for me. Finally he gave in and told me that Hugo Rune was dead. He couldn't understand why I fell about laughing.
All shall reap as the sow...except the amateur gardener
So, Timmeh, which character were you? 
All shall reap as the sow...except the amateur gardener
I would have to say Armageddon The Musical. It was the first one I read and left a huge impression on me ( it fell off the bookcase onto my head and the scar is visible to this day). I think I can safely say that it is the first book I have ever read that made me laugh out loud with tears streaming down my face. I try to reccomend it to every person I know and have even had a few successful converts.
My first book was "The Fandom of the Operator".
However, I agree that "Armageddon the Musical" would be a great book to start with.
I shall be lending it to someone in the near future in the hope of converting him. 
I recently lent that to our keyboard player, he seemed to like it. Has asked for "They Came & Ate Us" anyway
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Just have fun