How's about something that is neither, but is capable of the things both are famous for (usability and security)?
Postfix.
Postfix is as easy to setup/use as Sendmail (easier in some regards), it's sendmail compatible and is more secure out of the box than Sendmail.
It's also easier to setup than Qmail, security is about equal all though Qmail is known for it's security so that's arguable. Postfix is capable of using maildir which is one huge security feature in the mail server system. However should you wish to use the good old 'tried & true' mbox format, Postfix can do that as well.
www.postfix.org
Cool
