Prepaid sim or Pocket wifi?

hello. I'm traveling to japan on September for 17 days. I'm going to be in Hokkaido for a week and a half and then going down to Tokyo with a few stops on the way. In Hokkaido I'm renting a car and I want to use my phone for GPS (Yes I rented a GPS with the car but I prefer to have my Phone's GPS as well). I was thinking about using Waze or Google maps... so my question is - what is better to use , prepaid sim card or pocket wifi device? I'm worried that there will be no reception on some ares in Hokkaido so I want to be sure I get the best thing I could get . also, I need to use apps like Facebook and Whatsapp to communicat with people so I need your help with understanding which one is better for me.

Reception should be about the same. At this time I think service providers that use docomo as their backbone might be best for the region, but keep in mind that Hokkaido doesn't have the best data coverage. Consider getting used to using the car navi as your primary navigation tool and the phone as a backup since you don't want it cutting out while driving partway along your trip. Google maps is very good for getting around Japan btw.