I think you should return the s7 and get a refund if you are not satisfied with it. Then you can just wait until the s8 or the note 7 replacement. However I don't think they will rerelease the note 7.
Re: Why are note 7 catching fire and not edge 7 plus?
I think is a design flaw or a production defect. However, we won't know what is really wrong until Samsung makes a official announcement about it.
You may not have a choose because If Samsung discontinued the phone they may not update the note7. And depending on carriers and retailers there is a deadline to get a refund.