Domain names historically have been www.example.com , written also with the protocol prefix http://www.example.com , but in reality www. is optional, only example.com is actually needed.
www. is technically a sub-domain and sub-domains incur a small penalty in search engine optimization.
There is no right or wrong. What is important is that you choose one, and the other needs to be a 301 Permanent Redirect to the one you have chosen.
You also need to know that creating a server alias in your web server configuration, for example Apache or Tomcat is not a permanent redirect, in-fact it is technically duplicate content, with two web sites the same also incurring a penalty for search engine rating.
So what do the big players do. Here are a few.
Use www
- www.google.com
- www.facebook.com
- www.cnn.com
- www.yahoo.com
- www.myspace.com
- www.ebay.com
- www.plurk.com
- www.amazon.com
- www.fotolog.com
- www.linkedin.com
Do not use www
- digg.com
- wordpress.com
- identi.ca
Show duplicate content
- flickr.com
- chi.mp
- corkd.com
- vimeo.com
- garysguide.org
- engineyard.com
Curiously youtube.com uses a 303 redirect, microsoft.com, stumbleupon.com and craigslist.org a 302 redirect.
How do you check? Use a CLI tool such as wget.
$ wget www.google.com --2008-09-22 19:56:48-- http://www.google.com/ Resolving www.google.com... 72.14.205.99, 72.14.205.103, 72.14.205.104, ... Connecting to www.google.com|72.14.205.99|:80... connected. HTTP request sent, awaiting response... 200 OK $ wget google.com --2008-09-22 19:57:56-- http://google.com/ Resolving google.com... 64.233.167.99, 64.233.187.99, 72.14.207.99 Connecting to google.com|64.233.167.99|:80... connected. HTTP request sent, awaiting response... 301 Moved Permanently Location: http://www.google.com/ [following] $ wget www.facebook.com --2008-09-22 20:07:59-- http://www.facebook.com/ Resolving www.facebook.com... 69.63.178.12 Connecting to www.facebook.com|69.63.178.12|:80... connected. HTTP request sent, awaiting response... 200 OK Length: unspecified [text/html] $ wget facebook.com --2008-09-22 19:59:43-- http://facebook.com/ Resolving facebook.com... 69.63.176.140, 69.63.178.11 Connecting to facebook.com|69.63.176.140|:80... connected. HTTP request sent, awaiting response... 301 Moved Permanently Location: http://www.facebook.com/ [following] $ wget digg.com --2008-09-22 20:10:47-- http://digg.com/ Resolving digg.com... 64.191.203.30 Connecting to digg.com|64.191.203.30|:80... connected. HTTP request sent, awaiting response... 200 OK Length: 15322 (15K) [text/html] $ wget www.digg.com --2008-09-22 20:14:06-- http://www.digg.com/ Resolving www.digg.com... 64.191.203.30 Connecting to www.digg.com|64.191.203.30|:80... connected. HTTP request sent, awaiting response... 301 Moved Permanently Location: http://digg.com/ [following] $ wget twitter.com --2008-09-22 20:26:18-- http://twitter.com/ Resolving twitter.com... 128.121.146.100 Connecting to twitter.com|128.121.146.100|:80... connected. HTTP request sent, awaiting response... 200 OK Length: 2655 (2.6K) [text/html] $ wget www.twitter.com --2008-09-22 20:26:41-- http://www.twitter.com/ Resolving www.twitter.com... 128.121.146.100 Connecting to www.twitter.com|128.121.146.100|:80... connected. HTTP request sent, awaiting response... 301 Moved Permanently Location: http://twitter.com/ [following]
Professionally, I prefer shorter and simpler without www.
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