Discworld

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...