Fingerprint reader on the side is... That's going to be super irritating every time you want to just do something quick while the phone is on a table.
The whole fingerprint reader thing is going to be a bit weird regardless.
I use the example of when my phone is in the windscreen dock for my car.
The docking station will obviously cover the back, and mine covers both sides. So the only way is on the front.
I've thought for a while that if Apple can nail Force Touch, then in 1-3 years we could see the iPhone lose the home button, and the fingerprint scanner could develop onto the Force Touch screen.
In short, nothing is 100% ideal right now, but it depends how you use your phone predominantly.