Everyone seems to have their own preference - mine is Postfix. There is a nice
howto for installing it on CentOS; I imagine this translates to Fedora without too much difficulty. If you do not need POP/IMAP access, skip the part about installing Dovecot.
You should also look into setting up
Postfix restrictions and
greylisting to reduce spam. Be aware that using block lists (reject_rbl_client) can result in false positives.
pbl.spamhaus.org is quite conservative; if it isn't enough,
zen.spamhaus.org is a bit broader. The bl.spamcop.net list is in their words "
aggressive" so may not be a good choice. I personally run a mailserver without a block list at all - greylisting and the Postfix sanity checks do a very good job on their own.