From www to no-www:

RewriteEngine on

# 301 redirect to domain without 'www.'
RewriteCond %{HTTP_HOST} ^www.example.com$ [NC]
RewriteRule ^(.*)$ http://example.com/$1 [R=301,L]

From no-www to www:

RewriteEngine on

# 301 redirect to domain to 'www.'
RewriteCond %{HTTP_HOST} ^example.com$ [NC]
RewriteRule ^(.*)$ http://www.example.com/$1 [R=301,L]

I used to be no-www until I wanted to make use of pipelining and CDNs to speed up my site and wanted to control what content sent cookies and what didn’t. Using sub-domains allows you to do this.

What is your view on this? Should I stick with the non-www version or add the www?