i am using postfix as an MTA from the first time i had to setup an email server.
things i have noticed:
* syntax is very easy and understandable
* documentation is very complete and accurate
* easy to setup with a database backend (currently using mysql to store the domains/accounts)
* there is
postfix admin a web GUI which is pretty easy to setup and use for administration of you email server
and
here is a very good and self explanatory tutorial.
keep in mind that postfix is the only MTA i have ever used so i can't make a comparison to another one. others are more than welcomed to comment upon this.
/v