As someone who just made the switch in the opposite direction (I've been using Mail for multiple emails accounts for a few years) I'd strongly suggest sticking with Gmail's iOS app. My email experience on mobile has been much more enjoyable, Mail was glitchy and difficult to use/organize for me.
I use the Inbox by Gmail app on iOS and I really love it. I never got into the regular gmail app. Inbox is far better than the standard Mail client for gmail IMO.