I'm assuming you're picking between the two to buy. Don't have the G5 Plus, but I can try to give some input as I used many Moto phones in the past and have the SE.
The iPhone SE is pretty fast, as fast as 2016 Android flagship phones, the only negative for me is the somewhat small screen. Otherwise I recommend it.
Moto G5 Plus is a pretty decent midrange phone and it will run smooth as well because it use stock Android interface. One negative with the G series is the lack of NFC, which can be used for Android Pay, but have more useful functions on Android compared to iOS.
I would suggest you consider the original Moto Z Play (not the new Z2 Play which have very little improvements and is more expensive). This phone is getting cheaper now (see
Best Buy) and is not much more expansive than the G5 Plus. It have NFC, but also a bigger 3500mAh battery, compared to 3000mAh on the G5 Plus and Z2 Play. Z devices are compatible Moto Mods which the G series lacks.
However, if camera quality is important, the Moto G5 Plus and Z2 Play will have newer better camera than the Z Play.
Between the SE and G5 Plus, I would go with the SE because of Apple Pay.
Between the SE and Z Play, I would go with the Z Play. Although the SE will have a better camera and is more pocketable.