The Turbo 2 is pretty big if you're used to an M8. The S7 is probably a better size. Samsung seems to provide more timely Android and security updates to their phones, particularly as they get older, if that is important to you.
Personally, I hate the idea of a glass back phone. It's bad enough that the screens are glass - now you're doubling the chance of shattering something if you drop the phone.
The S7 is 32 GB only. Yes, you can get an SD card for photo and other media storage, but I prefer that my phone can store 64 GB myself.
Go to a Verizon store and try handling both. That's probably the best idea, to get an idea of the size and the display quality.