JR East Pass

Hi, my family and I planning to visit Japan for 13 days at the end of the year ( late Nov ). We would like to cover Tokyo, Yamagata, Ginzan Onsen and preferred to stay 2 nights at Tokyo before move on to Yamagata. Here are my questions:

1) Should I purchase a JR East Pass ( 5 days )?
2) or JR Pass ( 7 days ) to cover more city?

Thank you.

Regards,
Mr Q