I'm on the same Samsung boat, have an S5 mini (3 years now) and want to move away from it.

Battery-wise, the "best" one I've found is the Lenovo P2 which has 5100mAh (S8 Plus has 3500) but not sure if its hardware is any good. I'm planning however to get OnePlus 3t which has 3400mAh and seems like a better long-term choice.