Portsmouth is very peaceful and quiet if not directly on a main road. It is all very safe. It’s mostly residential, mixed with farmy areas and lots of water.

Your food choices are more limited as there is not too much commercial, but you can drive to Newport, Middletown, and Bristol quickly which all have great options. Plus you are close to the beach.

I can’t speak on Riverside as I never go there, but why not drive thoroughly around both areas and see what catches your eye :)

For reference I live in Newport so I am very familiar with the whole island.