I guess I don't really understand what makes someone a better writer.
Martin's story is better, his characters are better, he tells the story more concisely, his story is deeper and more realistic. His world is more authentic. There are tons of important and interesting subplots.
Robert Jordan is good at making you feel the passage of time. If a trip takes a month, he makes it feel like it took a month to read that trip. His story is extremely predictable and his characters are sometimes laughably bad. Basically every woman in his books is the same as every other woman. A bitch who treats everyone around her like crap and acts like her doodoo smells like roses yet none of the men around her will dig a hole and throw her in it like she deserves. I am fairly certain that Jordan(Rigney) wrote half of his book with his pants around his ankles. There is no sex in the books really, but I lost count of all of the times where a woman just had to be naked in front of a bunch of strangers and she was so embarrassed and ashamed. Hey, it's tradition to whip out our tits to prove we're women, let's do it! Hey, we don't have a lot of water, so let's all get naked and hang out in a tent together, no big deal. Hey, I have to go to this city in the desert to prove I'm smart and strong, I'll walk there naked! There are also several veiled BDSM bits that get quite tedious.
Martin has plenty of sex in his series, but for the most part, it actually serves as an important part of the story. There are a few exceptions, but no one is perfect.
Ugh, I get fired up about these books. I am coming off a bit too harsh on the Wheel of Time series, but it does have some really terrible moments. Overall, it's a solid story, though it is predictable.
I look at Martin's work with a little bit of a rose-colored glasses complex, and I acknowledge that, but I can't think of a single moment in the books where I rolled my eyes at the lameness. Mostly, it just captivates me. There are so many mysteries and subplots to think about. The story is far less predictable than anything else I have ever read. Many of the surprises have been spoiled, seeing as the books have been out for years, but it's still an amazing story.
If you want a quick and easy taste of his style and the world his stories take place in, check out the short story called The Hedge Knight. It takes place in the same world, but roughly 100 years earlier. Much simpler story as well, seeing as there are only two characters really.