In might be a theoretical advantage to not be rooted. But you loose a lot of functionality for that security "gain". Pragmatically though there have been plenty of malware exploits that can root your device as part of their incursion. So it's hard to believe that you are gaining much security by avoiding root on your handset.
Your device will never be completely secure. Most of your risk is removed if you make a best effort to only use apps from legitimate sources and apply security updates. If you are keen you can also install a antimalware app like lookout or configure iptables.