I tried switching to iPhone earlier this year, and tried Swiftkey and Google Keyboard Apps on it. It is maddening having to switch to the SYM screen and back to the ABC screens.
In Android, a delayed 'press' on a number key brings up a symbol like &, %, @, etc. Much more efficient!
Will Apple iOS not their keyboards to do this? If not, why? If they did, I would switch back.
(Apple's embedded keyboard doesn't even provide numbers across the top...at least Swiftkey does)
Since the keyboard is the main source for input on a smartphone, I've chosen stay with Android.