Questions about subdomains

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I bought a domain name where I am going to host my sites. It will be divided in three parts. One part for the site that has recipes, the second part is a blog and the last part is forums. I have a question about the best way to set the URLs. Is it better to do the following: http://www.example.com/ http://www.example.com/blog http://www.example.com/forums Or is it better this other way: http://www.example.com http://blog.example.com http://forums.example.com Which way is better and why? Thanks for your help.