Here is something to consider regarding different polling organizations, it considers "house effects", aka bias, and gives a grade on accuracy. Some pollsters are better than others, there are even some flunkies.
Five-Thirty-Eight Polster Ratings FiveThirtyEight’s pollster ratings are calculated by analyzing the historical accuracy and the methodology of each firm’s polls. Accuracy scores account for the type of election, a poll’s sample size, the performance of other polls surveying the same race and other factors. We also calculate measures of statistical bias in the polls.
