Both phone came from the same brand plus they have AI etc which make the picture colorful, but it really upto you which one really fits you.
Honor Play = Kirin 970 + GPU turbo which good for gaming.
Camera[Rear and front] = Good Lowlight and day light
Video[Rear and front] = Really good and also has stabilization.
Slowmo = 120fps
Nova 3i = Kirin 710 + GPU turbo, but Kirin 970 is more powerful.
Camera[Rear and front] = Lowlight picture is okay, but with the selfie is not good.
Video[Rear and front] = Doesn't have stabilization which your video will be noisy.
Slowmo = 360fps
Try to check TechBeans for YøùTùbé if you're not really sure about the Phone, but I suggest buying Honor Play.