They are both good O.S's but the choice depend on the user kind..
IOS have good optimization, security, and support from the producer...
but imho is too closed to customizations and comunications with not-ios devices, moreover doesn't have a wonderful modding comunity as android have (XDA).
Thats why i prefer android is fully customizable according to the needs of the user..
support nfc (that i love for contactless payments) bluetooth, infrared and any other form of comunication..
moreover as i've said above it have a great modding comunity that extend the device life for years after that the producer support is over..
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