Real Clear Politics uses both NBC/Survey Monkey and NBC/Wall Street Journal polls in their averages. Neither are credible since it turns out their chief pollster is a paid Hillary adviser.
http://www.freerepublic.com/focus/f-news/3479091/posts
Public Policy Polling (PPP) only work for Democrats yet in 2012 they were among the three most accurate polling organizations in their final prediction before the election.
The NBC News/Wall Street Journal Poll uses BOTH Democrat polling firm Hart Research Associates AND Republican polling firm Public Opinion Strategies.
Since realclearpolitics takes a simple average of up to ten national polls, any one poll’s findings impact the whole in a minor way.
My own way of using them is to take the seven most recent polls, throw out the widest and the narrowest outliers and average the other five. For this week, the NBC News poll is thrown out.