The fifth elephant. It actually made me read through all the other Rincewind books and then everything else I could find by Mr Pratchett. Loved his world building.
I really don't know which one I read first. It was either The Colour of Magic or Going Postal. Either way, I found the book in my school library, where I was told to cool down during sports after I fainted because we had a heatstroke.
As to my favourite book, it's between Lords and Ladies and The Thief of Time. Don't make me choose between Shakespeare and old Hongkong kungfu film tropes...
As a child my first introduction to Terry Pratchett was the wee free men as an audiobook, and then a few years later some kind person recommended Mort to me, which I loved. It took me a while to figure out that my beloved childhood Tiffany Aching books were the same as the new Discworld series that I had discovered.
How, with such a breadth of outstanding novels, am I supposed to pick a favourite?
I also can't remember which is my first, a family friend lent us everything up to The Last Continent in one go, and I read them all in a completely random order.
First is hard to remember, but was probably The Color of Magic which delayed my reading of his other books for a time. It’s not bad, but didn’t grab me like the later books did. Favorite is hard to pick. The Last Continent, Monstrous Regiment, and Guards! Guards! are all great.