720p is better than 1080i, though the difference is hardly noticeable.
720p is a progressive scan, much like 1080p.
That is why ESPN produces in 720p. Progressive scan is much smoother/faster which in turn, makes sports look better because of the constant motion.
1080i is interlace, which isn't as smooth. Also, broadcasts in 1080i aren't always 1080i, meaning there aren't always 1080 lines interlaced into the feed.
When the day comes that we're able to get 1080p, it'll be heaven though..
I found this:
To answer the question, it's important to understand the difference between 720p vs 1080i. A 720p signal is made up of 720 horizontal lines. Each frame is displayed in its entirety on-screen for 1/30th of a second. This is know as progressive scan (hence the 'p')The quality is like watching 30 photographic images a second on TV. A 1080i signal comprises 1080 horizontal lines but all the lines are not displayed on-screen simultaneously. Instead, they are interlaced (hence the 'i'), ie every other lines is displayed for 1/60th of a second and then the alternate lines are displayed for 1/60th of a second. So, the frame rate is still 30 frames per second, but each frame is split into two fields, which your brain then puts together subconsciously.
Most of the time interlacing works fine, but for fast moving images, such as sports like baseball and hockey it can cause problems which manifest themselves as a 'stepping' effect on-screen. Progressive scan signals don't have this problem and so are better suited to sports.
ESPN puts it like this: 'Progressive scan technology produces better images for the fast moving orientation of sports television. Simply put, with 104 mph fastballs in baseball and 120 mph shots on goal in hockey, the line-by-line basis of progressive scan technology better captures the inherent fast action of sports. For ESPN, progressive scan technology makes perfect sense.'
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