Sanderson just genuinely enjoys writing whereas I think Martin views it as a chore. If you follow Sanderson on facebook he near daily talks about how much time he was able to get in writing that day and you can tell he's bummed if he can't get several hours in.
Personally I'd rather have a good writer who is prolific and occasionally writes something great vs a writer like Martin who can't seem to be bothered anymore to write even if what he writes is usually marginally better than most other people. While Game of Thrones (the first book, not the TV show) is probably better than any book Sanderson has written the sum total of Sanderson's good far outweighs Martin thanks to five (soon to be six in a few weeks) Mistborn books, two (soon to be three in a few weeks) Reckoners books, two Way of Kings books, and a bunch of very good semi stand alone stuff (most of Sandersons stuff has loose connections much the way Stephen King's works all had loose connections).
P.S. For those who haven't read his Reckoners series it would likely be of interest to comic book fans. Its about a world where an event causes ordinary people to gain superpowers but those powers also warp the people to be evil and they take over and rule the world. Regular humans, known as Reckoners, fight back. Its a planned trilogy with the final book coming out in few weeks. It's classified under the YA genre but that doesn't make it any less fun.