Nagano or Sendai?
 

we are planning on going from hakone to Nagano or Sendai back to Nartia (departing)

which would you chose (Nagano or Sendai) and why? and going from hakone would one night at either of these be enough?

also where would you recommend staying?

I'm wondering why you would want to head to either of these for one night? Although Sendai is a pleasant city, and Nagano is a fun place to go skiing, neither is really interesting enough to go that far out of your way. I'd spend the extra day in Tokyo or on a day trip to Nikko or Kamakura.

The shinkansen from Tokyo to Sendai can take as little as 101 minutes (06:52 to 08:33). The shinkansen from Tokyo to Nagano is about 85 minutes. So it's a matter of deciding whether 3 or 4 hours is worth it for an overnight stay.

Taking a tour boat around the islands of Matsushima near Sendai would be one thing to do. But there are a variety of other options in both areas.

Just a quick browse at jnto.go.jp gives info for visiting each area. For Nagano, here is a "3-day Model Trip", click on each picture for a description of the days's activities:
http://www.jnto.go.jp/eng/RTP/joshinetsu/index.html

For Sendai, here is an itinerary from Nikko:
http://www.jnto.go.jp/eng/RTP/Southe...oku/index.html

At the bottom of the Sendai page, it shows Access, from Tokyo to Nikko, from Tobu Asakusa Station. That's the Tobu rail company, so a Japan Rail pass would not be useful on that line. But that Asakusa Station is going to be near the place that you are staying in Tokyo.

Here is a 3 day itinerary:
http://www.jnto.go.jp/eng/RTP/Southe..._course_a.html

I agree that Sendai is not really worth traveling to from Tokyo for just one night. Nikko would be a great place for a one night trip.