Q: best export mode for fce movie to email?

Usually video files are way to large to email.

I usually upload to Dropbox or Vimeo and let people download from there.

That being said, H.264 is the way to go.

Export your video from FCE using the current settings. Then open it in Mpeg Streamclip and convert it to H.264

x

How long is your video?

Assuming the email limit is around 10MB you would get  about 1 minute of video size 640x360 or 4 minutes of 320x180.

The latter would give very low quality.

Much better to upload to a web storage site in higher quality as Studio X suggests.