Which choice is better: site.gr or www.site.gr?

Between the two options it is best to choose the site.gr, because it is faster and easier for the user to enter the address. If alternatively you want your website to play with both ways there is this option too. All you need to do is open the .htaccess file and add the following:
- RewriteEngine on
- RewriteCond %{HTTP_HOST} ^site.gr
- RewriteRule (.*) http://www.site.gr/$1 [R=301,L]