Terry Pratchett. I loved the way he found the absurd in reality and could just twist it slightly. Reading his books was like watching humanity and it's obsessions in a hall of mirrors. It think he was far deeper than those who would read him for the humour understood.
I'm not good at having a favourite whatever. If I think of one of something I then think of another, then another etc.. Terry Pratchet was a great favourite of mine with his Discworld series (especially the early ones). Then there's Douglas Adams and his Hitchhiker's Guide series. Prior to that there would have been umpteen science fiction/fantasy writers. And before that, classical authors. And I'm sure I've got more that I just don't recall at present.
If i enjoy a book, i tend to read more from the same author, sometimes to the point where i have read most, if not all of their novels. Harold Robbins, Leslie Thomas, James Patterson, Douglas Lindsay and, more recently, Mick Herron, to name but a few. Stephen King is the one constant since about '75, and i have read almost everything he has written in that time. Last night i began reading one that had slipped by me - The Colorado Kid - from 2005.
Think there's a lot of "snobbery" about books and authors. Favourites for Desert Island Discs were The Bible and Shakespeare which I very much doubt anyone actually read. My taste has changed through the decades from Enid Blyton to Terry Pratchett, Tolkien, Nevil Shute and everything in between.
Like a few others, I love the absurdity of Terry Pratchett, Douglas Adams (Spike Milligan, Robert Rankin) and the escapism of Tolkien, Howard or Pullman, but if I have to name just one, it'll be Iain Banks. His real world novels had such imagination and originality, and his Sci-Fi combined the best of Clarke and Asimov with the imagination of George Lucas.
Rudyard Kipling and George Orwell. (Sorry can't decide between them). Favourite poem The Rivers Tale and favourite book Animal Farm. Also like Alexander McCall Smith for the No. 1 Ladies Detective Agency.