What's the biggest draw of GrapheneOS apart from de-googling? Does it have a better battery life? And compliance with NFC payments?
The ability to sandbox Google Play Services (if you need it, but realistically, you probably do) and to simply not assign it more permissions than it absolutely needs is awesome. I run it with very restricted permissions, where it by default requests every single permission it can. In stock Android, it has all those, and you can't limit it. Just that is worth it for me.
If you actually degoogle, supposedly battery life is better but if you start adding back in sandboxed play services, you lose some of the gains.
Greatly improved privacy and security and end-user control of your phone and its data. In those areas, possibly the best option, though iPhones might be better in security (not necessarily the other two areas) - Apple has a slightly bigger budget and a few more engineers, and directly controls the hardware.
It will depend on your banks/services. If those apps strictly implement Play Integrity API, you won't be able to use them on Graphene OS
For me it's the added security features: per-app network permissions, scoped storage/contacts permissions, and a bunch of system hardening measures.