There are a lot of ways to measure competitive balance, and I have chosen to use a simple measure called the Noll-Scully Competitive balance measure. By competitive balance we are looking at how well a league's standings are in relation to a league where wins and losses are determined randomly. Here is a step-by-step guide if you want to calculate this on your own. As a reference, here is the Noll-Scully using a sample or a population for the NFL from 1981 to 2012.
For the NFL in 2014 the Noll-Scully was 1.562 (population) and 1.587 (sample). If you click on the link in the last sentence above, you will notice that the NFL's competitive balance for this past season is very similar to recent seasons.
Since the 2000 NFL season, competitive balance in the NFL has been fairly stable as shown below: