Should I use www. or not in my main URL?

[NetPicks]

I have backlinks coming into my homepage, which has both a www. URL and one that's merely http://mysite.com. Which is the preferred URL for best optimization for search engines and how do I find this out?

[Thos003]

For character sake I would opt to not use the www and have it redirected. But once you have decided make sure you are consistent. You can advertise with either, it's more the actual linking that makes the difference.

[winlynxtp]

I started out as a Windows guy using IIS at which point you want to setup the primary domain account then setup the dns alias to point to the primary domain.  This way there is no marketing involved because they point to the same location.  When setting up a webmaster account I use the www but it really doesn't matter because it still points to the original domain.

[PeteGregory]

As has been stated it doesn't matter which one you choose, but since you do have links to both, I would pick the one with the better link profile. The one with the most or better quality links would be my choice.

[NetPicks]

Thanks! I threw a redirect from the http:// to the http://www. address.

[blu42media]

Theo's on the money here... it makes no difference to the engines.

If you need help deciding, check out which homepage (with or without www) has the higher rank and roll with that one!

[Theo-NL]

Both are equally good and neither are preferred more or less by the search engines. Just choose which one you like more (for whatever reasons) and redirect the one you don't choose to the one you do.

My personal choice is www as it looks more 'classic', but various reasons could be given for the non-www as well (such as the fact that it creates shorter URLs for example when Tweeting one)