What should I set my domain setting to?

[damon1212]

In Google Wemnaster tools, I have the option to set it to either have as default the "www" or without it.

What are the pros and cons of one way or the other . . . or is this a way more complicated question/can of worms I have opened?

[AlanBleiweiss]

It's based on whether you want your site to be associated with the www version or the non www version.  So if you routinely promote your site with it, focus on inbound links with it, and have that as your default user experience (such as with setting up a redirect from the non-www version) then that's what you should set in GWT.

It's essentially a way for Google to help properly assign the value of non www inbound links to the www version if that's what you designated.

Personally I no longer use www versions and recommend clients skip them as well because that's 4 less characters to have to get into ads, on business cards, type...

The most important factor though is to ensure you've got 301 Redirect functionality set up from the one you don't want to have used.  GWT just adds a bit more value if you set it there.

[andresgmontero]

I think Alan has a point there based on adding the URL to advertising, I think is more of a branding issue, in my case I like the www., it won´t really affect your SEO, but whatever you choose, that 301 is very very very important, also make sure the canonical tag is set to the version you choose.

[QualityHosting]

Personally i feel that people (not us) don't understand you don't need the www. part of the website URL.  So do to social engineering I would leave that part in.

The only pros and cons that i could think of is if you don't specify the specific version.  You should also do 301 redirect in addition simply because not everyone uses google to search for website.

[MikeGracia]

Same opinion as everyone else here, it is not just about webmaster tools, you should use a 301 redirect from one versionm to the other too

As for whcih version to use, in my opionion it doesn't matter from an SEO standpoint which you use really, so it's down to a business decision based on what you feel is aesthetically more pleasing, or more useful to you. WITH ONE POSSIBLE EXCEPTION.

If you are in the situation that you have lots and lots of quality links to either version (www or non-www) then I would tend to lean towards that version. Obviously so long as you are putting a 301 redirect (are you on a linux server by the way?) then in time the weight of the links from one version (www or non-www) should be passed to the other version, via the permanently moved header status that Google will find. Even so, to keep things running smoothly, personally, I would go for a balance between what I think looks best, and which version has the most backlinks at present.

Whichever you choose, setup the 301 from the other version, to the version you go with.