Although each MTA provides similar functionality, I'd still avoid sendmail because of security issues and the fact that sendmail configuration lacks sanity. Personally I'd recommend postfix due to the fact that it is well designed (modular), extendable, secure, and uses less resources then sendmail. Qmail is another good alternative.

I'd say the thing which would be the biggest consideration would be what platform you plan on running it on. Solaris, Linux, BSD (possibly windows) all have slightly different considerations.