I'm British and have lived and worked in Spain for several years. I continuously correspond in English with people from many countries. I find that emails written by people from non-English speaking countries commonly end with 'Best regards', while this valediction is uncommon in correspondence with native speakers.
The questions, answers and comments proposing the use of 'best regards' on this forum and other places from my Google search appear to be posted predominantly by people with non-English sounding usernames.
I have nothing against 'best regards', but my recommendation to advanced English users in non-English speaking countries who want their emails to look as 'native' as possible is to substitute 'best regards' with 'kind regards' or 'best wishes'. Is this a valid suggestion?