Interesting stuff. Goes to show it's far from fool proof.
http://www.nytimes.com/interactive/2016/09/20/upshot/the-error-the-polling-world-rarely-talks-about.html
Nate Silver rates
Marquette: A
Echelon Insights: NR
Berland: B-
Stanford University/Columbia University/Microsoft Research: NR
NYT Upshot/Siena College: A