Top mail servers

[Srivastava, Abhay]

Folks,
    I am in the process of hosting a site on Tomcat on Ubuntu. I will be
also running a mail server. As per your experience which are the top
mail servers? While googling I came to know these names :
 
Sendmail
Postfix
 
 
I would appreciate if you can give your inputs.
 
Thanks,
abhay