Well, I really don't care much for cPanel, as all the bugs and security holes. But I would think DirectAdmin is pretty secure, since it's far more stable.
Also, the control panel is as secure as the person managing the server. Meaning, just because a person has a secure CP, it's still is up to the Admin.
What I hear is Ensim is the most secure. I have not played with the new 4.0 yet but looking at it there are security settings the admin/reseller can set when creating a new domain.