For the monthly service? Amazing Instant is almost identical to Netflix. I was considering getting both when I dropped cable to have 2 quality cheap sources... but literally 75% of what is on one is on the other.
I'm a long time Amazon prime customer and am extremely happy with it. Lots of free movies, but I should take more advantage of it than I do. I shop on Amazon all the time and avoid SOOO many errands with Prime.