There are some amazing Sci Fi writers out there that can have you believing the most outragious concepts as if you've grown up with them. But there are also some incredibly lame writers who still seem to sell books?!?
So...
Sticking to my personal fave genre, Sci Fi, the question is whos the best? Obviously we all have our own way of reading, accepting or absorbing ideas and concepts so theres really no such thing as 'The' best, mearly various perceptions of mind.
I'm really liking Peter F. Hamilton. He can take you places and then explain how and why in such a way that theres no imaginative effort at all when I read. He enables me to flow through a cinima of mine own imagination as easily as watching a brilliant and compelling movie. The difference is of course the images that come to mind are, all though triggered by his imagination, entirely of my own making!