When it comes to picking the correct domain name extension it really doesn’t matter. The only thing to consider is if you choose a country domain extention, you’ll get better ranking in that countrys search results. The only reason that certian extensions are more common then others in search results is because they’ve been around much longer.
Some domain extensions are only a few years old compare to others that were used almost sine beginning of the web. You do want an extension people can easily remember. Web surfers are more prone to remember *.com, *.org and *.net URLs then lets say *.us or *.ws extensions. What you need to remember is the extension will not have any affect on your search engine positioning.
If you register news.com or news.ws they will both have the same equal ability to rank in the search engines, one will not have any higher value over the other due to the extension. It should be noted that web surfers would probably remember the *.com version over the other.