I like reading a lot, and there are many writers that I like, but there is just something about Terry Pratchet that I find most excellent.
Could say something similar about George R.R. Martin, since I've read most of what he wrote, and all of it was pretty interesting. Of course (as I write this), we still have to see where the whole Ice and Fire thing will end up :)
I used to (and sometimes still do) read a lot of SF, like Clark, Asimov, Pohl, Anderson,...
One of the early SF books I've read was "The Ring" by Daniel Keys Moran. It made a very good impresion on me, being like life, with no perfect charters, nothing going perfectly. I read it a few times and still found it to be pretty good. They say it is the authors worst book, but I can't say 'cause I haven't been able to get others. On retrospect, it had it's flaws, mainly about ordering the storytelling a bit around, but I still think it had some very nice ideas and I think fondly of it.