I prefer to use MIME::Lite for generating the email itself and Net::SMTP for sending the email. MIME::Lite for me is a no-brainer because it makes it totally painless to add attachments, etc. I like to use Net::SMTP when it comes to actually sending the mail for a few reasons:

• better error handling - you are controlling the SMTP exchange so if there are any errors anywhere in the process you can handle them exactly how you want to (you can switch to a fallback mailserver, queue the message for later, or something else).
• significantly faster than forking off a sendmail process.

The power of Net::SMTP comes at a price: more code. It won't be a one or two liner to send mail anymore because you'll need to handle the complete SMTP transaction with error checking, etc.