well with this waterproofing probably back to an iPhone :)
Security+convenience+waterproofing are the key characteristics for me and the iPhone hits those fairly well (now).
I've tried various androids but from what I've seen of their security/update policies the only way to get a good level is either use a nexus device or manage OS patches/upgrades yourself, even there I think that Android is still some way behind iOS on the security front.
That said I'm very much not a fan of Motorola's attitude to security patching http://arstechnica.co.uk/gadgets/2016/07/motorola-moto-g-z-m... which is one reason for me to want to move off the platform.