Sendmail is the default mail-server software for FreeBSD, but you can easily replace it with one of the other MTA (for instance, an MTA installed from the ports).
There are various alternative MTA's in the ports tree already, with mail/exim, mail/postfix, mail/qmail, mail/zmailer, being some of the most popular choices.
Diversity is nice, and the fact that you have many different mail-servers to chose from is considered a good thing; therefore try to avoid asking questions like ``Is Sendmail better than Qmail?'' in the mailing lists. If you do feel like asking, first check the mailing list archives. The advantages and disadvantages of each and every one of the available MTA's have already been discussed a few times.