This thought never crossed my mind till today, so here goes.
Consider i want to optimize for the keyword 'webmaster forum'(assumption).
For a domain, to reap the EMD benefit it would be ideal to have something like
For a folder or file, the ideal way to get the onpage benefit of 'keyword in URL', i'll have to have the URL as
However for Subdomains, which is the best way to have the keyword in it??
1) Seperated by a hyphen as in :
2) No keyword seperation as in :