301 Redirects, www and Non-www

[megri]

301 Redirects, www and Non-www
There are lot of talk's that which is best version of your site yoursite.com or www.yoursite .com as search engines consider them as two different version
So we have to decide which is best with or without www as it may have following
1. Duplicate contents as both version has same data
2. Might this give the site an overall boost in PR?
3. What is the short-term effect of making this change.?

My opinion is to use with www