Originally Posted by
fliesdelta
I've used the SmartEX app with zero problems. It seems to Just Work with all regions. Pick origination and destination, then if you're within 30 days of date of travel pick your seats, then pay. That's it. My first trip to Japan was last year, I bought the first set of tickets (Tokyo - Kyoto on the Nozomi) while still at home in the US.
SmartEx or JR Central should work for OPs itinerary. SmartEx excludes JR East and JR Hokkaido coverage (which currently only has shinkansen to Hakodate) so if you're going North-ish from Tokyo towards Sendai or Niigata on the shinkansen, you'd want to use JR East eki-net in English. Next trip
I think eki-net JP version allows national all regions booking to (mostly) Just Work but requires JP ability. Smart-Ex offers advance booking discounts which I don't think JR Central or eki-net JP do. The two eki-net language variants require different account registrations.