Appstore Ratings: Who gives better ratings, freemium users or paying users

Our standard user is free, but paying users can do more. I'm trying to figure out if it makes sense to not prompt "Rate us" screens for paying customers. On one hand they have more features, and since they are paying they must like it. However, as paying users their expectations are higher and so they might be less generous. Also with more features they have more to complain about.