Actually 720p is IMO superior to 1080i as 1080i is actually only 540 lines of vertical resolution at any given time as it shows one set of 540 lines, then the other. But does it so fast that the eye cant tell. Thats interlacing. But with 720p you see 720 lines of vertical resolution at any given time. Progressive scan anything is always better than Interlaced. Unless you are talking 480p. then 1080i would be better.
Not on LCD/Plasma screens though. What they do is to take the two frames of 540 lines each and build the single frame of 1080 lines. So what gets really cut is the frame rate. In half. So the 720p progressive is still better. Also because to see the difference between 720p/1080p one needs to be close to the screen. After few meters the difference has gone. There is a chart explaining it in this article:
http://mobilitydigest.com/why-1080p-doesnt-matter-get-over-it/
That goes especially for very high screen resolutions of PC games. Unless one sticks his or her nose to the screen they are perfectly useless. But true, many PC gamers do stick their nose into the (small) display. Pretty unhealthy.