I would rank avoiding heavy congestion over tolls and grades.
I'd like to say that's easy, but it's not. You can decrease your chances of heavy traffic by avoiding rush hour on any major highway, but all bets are off if somebody does something stupid (which is daily). IMHO you need to develop the mindset that traffic up here is unavoidable. However, that said I think there might be a route through VT & NH (Route 2 I think) that may be slower but with less traffic. Someone else can probably help on that one.