Flamebait question, but I happened to configure both (repository versions) recently, so here's one opinion. Both are useable, and used. Exim is sold as easier to configure, but IMO it doesn't deliver on this - probably simple config is just an impossible thing for universal SMTP MTA. On the other hand, Postfix has larger internet share and more resources on the web dedicated to it. Therefore I usually go for postfix (once you learned it, it's not that hard), and only use exim if there's no postfix in distribution repository. --
With Best Regards, Marat Khalili
