I've test driven all these and the Prius V is louder if you don't mind; more so than the Prius. Prius V bigger perhaps but do you like the style, interior, sound, etc.? It does have the reliability but the Kia does have a 10 year warranty even on the battery (at least this is what I have been told). If you plan on keeping the car that long, that may be a consideration and resale not an issue. If this first year Niro is a flop, well....we all know what that means for resale. Niro was a quiet ride. Test drove FE today but will be testing the Touring this week with the larger wheels. NOTE: Any reliable crash test results yet on the Niro?
The Prius does have nice handling, etc. but you either like the looks or not. No vehicle is perfect; depends on what you are purchasing the car for and what your needs are.
Don't overlook the new Hyundai Ioniq coming out end of this year. You may want to hold out for that. It has nice styling and could be competition for Prius but again, no history yet.
The Niro is different in that it is trying to appeal to the crossover market which is a hot segment now. Each has their own niche and will appeal to different people for different reasons.