What's the best Atlantic to Pacific route?

I'm new to this site, and I'm planning a (roughly) 10,000-mile drive this summer, from Pacific to Atlantic across Canada, and back across the US. The trip will be my eighth across the continent and the purpose, in part, is to log and blog the fuel efficiency of my new Jetta clean diesel (I'm expect about 50 mpg). I'm still mulling about the route to come home. I've been across the main more northerly routes (Highway 2, I-90, etc.) and I'm thinking maybe Highway 50 across the middle of the country. Any thoughts on this, or any better suggestions to consider?

I think it would be great fun to do US Hwy-50 across the United States.