I think Williarob was able to explain it better than I could. It is best to capture at the original source of the media: 480i @ 29.97fps. I don’t think real-time capture software can IVTC as good as AVISynth in post.

For video-sourced material maybe capturing at 60fps is good, but if I had to guess I’d say for film-sourced material capturing at 480i 29.97 is best. The 24fps movie is slowed down to 23.97 during the telecine process. Thankfully there are programs out there that can detect 3:2 pull-down pattern and get rid of the extra fields.