I posted a link to Chuck Wendig's blog a while back, where he talks about how a lot of the best writing right now is happening at the YA level. This article from the NY Times opinion page addresses the same issue, and the author provides some opinions as to why he thinks this is the case:
http://opinionator.blogs.nytimes.com/2013/10/28/junior-varsity-is-where-the-work-gets-done/?_r=0
http://opinionator.blogs.nytimes.com/2013/10/28/junior-varsity-is-where-the-work-gets-done/?_r=0