I've also used both.
I agree with what 8588 says.
Netflix "throttles" high volume users.
Blockbuster has gotten better with the disc quality.
Netflix has better selection and larger quantity instock.
also consider
GreenCine | main member - Video-On-Demand, Buy and Rent DVDs
If you like hard to find movies( foreign, artsy, or just stupid movies in general).
If I had to go back, I would choose blockbuster because they give you free instore rentals every month.