Going to be gathering some fast action footage, motorcycle racing, which would be better 720p? or 1080i?

1080i will produce smoother pans when you whip the camera to follow the action.

There is a great article about the ongoing evolution of video technology in the most recent "Videography" magazine. What it reveals is that your question is incomplete. It only addresses the acquisition phase of production. The second half of your question should address the playback display.

What display do you expect your footage to be shown on? NTSC interlaced CRT? LCD/DLP projector? 1080i HD monitor? Newer display devices, like projectors and flat panels capable of progressive video, exaggerate the temporal artifacts of interlaced video.

Will your HD source be scaled down to SD for display? If so, an interlaced video source presents certain advantages and problems during the down-rezzing process.

The choice of playback display will best dictate your choice of acquisition format.

Anyone else wish to comment on this?

On another tack: Consider a faster shutter speed for sports acquisition. Perhaps 100/sec to 200/sec.

ouptput to broadcast HDTV (prolly 1080i) but may need to output in 720p. I figured 1080i would be better for fast action, and would transcode to 720p if needed.

Then I would suggest 1080i for it's faster frame rate. Couple that with a faster shutter speed and you'll be off to the races.

You might take a look at some NTSC racing footage and see what they are doing with their cameras. Their aesthetic and technical choices of framing, focal length, movement, interlacing, and shutter speed should directly translate to the HD realm.

HDTV 720p is 60-frames per second progressive. 1080i is 60 interlaced. 720/60p is objectively better for fast action. Perhaps you're referring to JVC's fake HD at 720/30p, in which case the FX1 at 60i would be better.

I bet you're right. I was confused by that non-standard.

Yes, the 720-60p would be better.