Subdomain or subdirectory for vbseo and 'google'?

Hi,
what is the best choise?
To have a forum vbseo powered in a subdomain or in a subdirectory?

Google or similar give more relevance to the subdomain that it is considered a indipendent web site, or a subdirectory that it is considered a page of a web site?

http://forums.mydomain.net

or

http://www.mydomain.net/forums

??

Subdomains are considered as different sites. I will only use subdomains when i serve different contents on each subdomain but mine is a personal preference.

Very Clear.... thanks