What should I set as Preferred Domain Setting In Webmaster Tools

[msaqibansari]

I have some confusions over preferred domain setting in google webmaster tool.

I have my main domain www . mysite . com
I also have a blog at blog . mysite . com

My question is for my main site should i select preferred domain as www as my site can only be accessible with www and 301 redirect without www
or should i leave it and set no preference? What is the significance of this setting?

I presently selected my main domain as www but some days ago google offered me my site without www to add in my domain list, although it is not accessible and 301 redirecting to www version. How google found and offered me this version of site?

Is present setting is OK for me to select www for main site and without www for my blog?

[piatkow]

Its very useful for people who are using cut rate hosting services that don't permit redirects.

[youfoundjake]

I would probably recommend that you use www.mysite.com with a 301 from mysite.com, and keep the blog at blog.mysite.com.
you can always try a google search of [site:mysite.com -inurl:www] to see what google has listed for your site.