Which MTA to use?

["Brooks R. Robinson" <chance@scholar.cx>]

Greetings,
	I am looking at changing an in-house e-mail system from an ugly combination
of outsourced collection/forwarding and JSMail on an NT server to linux.  We
have an ADSL line coming in, and I can handle all of the DNS and network
stuff through the firewall, but I drop the ball at mail.  We have about 100
clients using Microsoft Outlook, but our legacy address format is
first.last@domain.com.  I can't change the address format, and I'd like to
leave POP3 in place.  Which MTA is the best given my limitation?

Thanks,

Brooks