How to stick to only 5? Perhaps by listing the first 5 that come to mind.
Terry Pratchett for being hilarious, for shamelessly borrowing plot-lines (ok, parody, I get it) and for getting more political as he went along.
Neville Shute & George Orwell – the two whose ‘complete works’ I would most like to own – atmosphere, style, content.
Raymond Chandler for consistency of voice, and best use of simile anywhere ever.
Dr Jane Goodall, because I need to have at least one non-fiction writer on the list – and she is the one I go back to and am always encouraged by.