I started reading the books after watching the first 3 seasons. Read all of them within a month, they were that good. Continued watching the show after I finished the books and after season 4, the show started to become kind of ridiculous. Clearly the books is what made the show great but with no new material we had to rely on D&D’s own creativity to continue the show. It’s definitely suffered as a result and although I still enjoy it (despite the ridiculous storylines that occurred especially in season 6 and 7) I have a higher anticipation for the next book ( if it ever happens) than the new season.
So basically, the books are better.