CCNA has been the most useful to me -- if you want to go security, I'd recommend taking the CCENT and then the CCNA security (bypassing the CCNA Routing and Switching)... unless you want the CCNA R&S as well.
No one really cares about Network+ or Security+. I've had both and frankly they're not really anything special. CCNA at least lets your employer know that you're skilled in one field.