I've used both. I had bad experiences with Blockbuster and quit to go with Netflix. I've been using Netflix now for almost 2 years and it is stellar. Like others said, my turnaround is 3 days. I mail them out on Monday, Netflix gets them on Tuesday, by Wednesday I have new disks.
They do throttle you if you rent too many new releases per month and return them too fast. I have found a workaround for that....I upped my subscription to 5 disks instead of 3. Then I just asked for 2 documentary titles and kept them for a month. I was able to turnover the other 3 disks much faster and had no problem getting all of the new releases. I have since dropped down to the 3 disk plan again, though, so can't say for sure if the trick still works.
Another thing you can do that might speed up turnaround times: when you put the disk back into the Netflix envelope to send it back, most people put it right-side up. That's fine, but if you look at the front of the Netflix return envelope, there is a little window there. If you flip the disk around so that the barcode on the inner disk envelope is showing through the window on the outer envelope, your return can be processed by a machine instead of a person.
