This is going to absolutely be a 'personal choice' thing.
Wordpress is easier to use and understand, but in the same, there are a ton of exploits because of vulnerabilities in plugins (not the core WP system itself).
Haven't played a ton with Joomla, but it's not bad, just takes a bit more getting used to than WP.
Tom Whiting, WHMCS Guru
Linux problems? WHMCS Problems? Give me a shout
Check out my WHMCS Addons
+1 - 866-546-8914 / skype - admin_139201 / twitter/facebook - @whmcsguru