I posted a similar question about this earlier but it's a two part question. First I was curious about which to use in directories and backlinks but here I'm asking which to use in webdesign. Do search engines only look at what comes after the http or www so maybe it does not make a difference which to use or should I change the design of my site so that I'm using specifically and only one of the following: (www) (http://) or (http://www) Also, how do I make the changes to my site?
Change it so it's one or the other. Search engines will consider them to be 2 independent sites with duplicate content. It's relatively easy to set up your .htaccess to force visitors from one to the other. Some users will be spooked by the lack of www so consider the typical web-savyness of your site's visitors when deciding which to use.