Seattle -> NY or New England loop?

My wife and I have about three weeks to travel. We need to be in upstate NY at the end of the trip so either Seattle to NY via Yellowstone and Nashville or we are going straight to upstate NY and then doing a three week loop of New England. We've never been to that part of the country before.

It will be mid-June to just after Independence Day.

Any recommendations of which route to take? What to see in those areas?