Best camera settings for importing footage into iMovie?

The camera settings would depend on what use that you intend to make of the movie, and whether you have a lot of fast motion in your clip.

Assuming that you want to burn a good quality movie: Import with format H.264, Mp4/AAC, clips with 1080p resolution at 30 fps or 60 fps, or with 4K resolution at 30 fps (iMovie doesn't do 4K 60fps). A frame rate of 30 fps is fine for most purposes. If your video has a lot of fast motion in it, or you intend to use slo mo, then 60 fps would be more suitable.

For audio, iMovie does the lossless settings of aiff and WAV, or the lossy settings of Mp3 and AAC. It accepts and outputs 48000Hz.

When exporting, I would use the "Good" quality resolution setting. The "Best Quality (pro res) setting produces a 4x size file with no noticeable difference in quality for consumer use purposes. "Best Quality" is mainly for professional quality that might require intricate editing.

The above is my opinion. Others may chime in with other suggestions.

-- Rich

What camera?

As Rich said, not all cameras support all formats.

What you *don't* want to do is save things in formats like (for Canon) Clog3 which *require* colorgrading and look up tables to get useful video. iMovie doesn't play that.

And if this is really that important to you, you might want to step up to FinalCutPro. iMovie is a free consumer app. It has good results, but it is not professional.