Question

When passing Contact data for multiple Contacts, should I put each Contact record on a different row? Or is it okay to include multiple Contacts in one row?

Answer

There is a negligible difference in speed of import between passing multiple Contacts in one row, or placing each on a different line.

For ease of troubleshooting, however, it's a good idea to put individual Contact data on separate lines.  That way, if an error is returned in the FTP confirmation email, it will be easier to identify the culprit.