It depends on what kind of material you're watching also. The real advantage to progressive scan (the "p" in 720p) is that the integrity of the image is basically maintained even when there are periods of fast action. When frames are displayed as interlaced (the "i" in 1080i), you'll get a combing effect during action scenes. This is because on one refresh of the screen you'll get lines 1, 3, 5, 7, 9, etc, and on the next refresh you'll get lines 2, 4, 6, 8, etc. With progressive you'll get the lines of information in sequential order, painted along the top of the screen to the bottom, so at the very worst you would see only one visual rift on the screen (for example when the new set of lines 1 to 325 meet up with the old lines 326 to 720, you would see a rift between line 325 and 326.)
I personally use 720p even though my TV maxes out at 1080i. If your TV is under 50", you won't even be able to tell a difference between 720p and 1080p from a normal viewing distance. There is a great article about this on CNET. If you're interested, I'll pass along the link.
-Dusty
