Niseki/Hokaido

It largely depends on your destinations of course. But Hokkaido is BIG, and many of its best places are inconvenient to get to if you don't drive. If there was any place in Japan where renting a car makes more sense than taking the train, it would be in Hokkaido. But again, it's up to where you are going.
Just remember that fuel is quite expensive, the tollways aren't cheap either, and there are very stiff drop off charges if you turn in your car at a different city than where you rented it.

You might look at these sites to help you:

http://en.visit-hokkaido.jp/

http://www2.tocoo.jp/en/index?

https://www.japan-experience.com/car-rental-japan

http://www.e-nexco.co.jp/news/hep/

http://northern-road.jp/navi/eng/index.htm

Thank you so much for this information. We really appreciate it. Aloha, gail Fujimoto