The G4.
Because the microSD card slot is extremely useful for me, along with the removable battery.
I love the Edge too, but find that the lack of expandable storage is problematic for me and it's too expensive for what it does compared to the standard S6.
I don't judge battery life through benchmark lab tests. It's obvious that the S6 can last longer in a lab, but for some reason, the G4 eclipses it in real-world battery usage, according to reviewers, which matters way more to me than some lab test. Also, the G4 seemed to be a bit quicker in real-world tests, probably due to optimization.
I love both phones, but ultimately, the G4 won me over.