Either one protects you from outside threats, but Android does allow you to do more damage on your own.
If you're smart enough to not install shady apps and give them the rights to absolutely everything, it doesn't matter which one you use, but if your parents or grandparents are getting up there in age and are prone to just clicking on things that look like they should be clicked on, iOS might be safer for them (Android's workflow for installing apps from untrusted sources is just too simple IMO).