SEO : Domain Types

While the internet technically functions by using IP addresses (eg. 187.435.11.128) assigned to servers, we use domain names as the friendly way to access the website content located at the IP address (as typing in www.msn.com is much easier and more memorable that typing in 187.435.11.128, for example).

Generic Top Level Domains (TLD)

For search engine ranking purposes try to use a Generic TLD, such as:

name.com
name.net
name.org
name.info
name.us
name.eu
name.cc
name.ws
etc.

Note they only have one '.' and one word after the '.'

Sub domains

Typically sub domains contain more than one '.' like this:

name.us.com
name.job.com
etc

These are derivatives of the top level domain names US.COM and JOB.COM

While subdomains function like top level domains, but they are risky for search engine optimization purposes, because:

Some engines may not rank them as highly as top level domains
You may suffer from bad neighborhood (where you are tarnished by someone else using a similar domain)
if the Registrar ever goes out of business or decides to sell the parent name then your name (along with your website & email) will cease to function immediately, potentially without warning.

If you serious about getting to the top of the search engines and staying there, you should stick with Top Level Domains.