MHT is great. UA at MHT is a disaster. I live about 10 minutes from MHT and will only fly UA out of there with a 2+ hour connection and am taking an early morning flight.
You can't beat how nice and easy MHT vs. BOS. But I think if anything needs to be cancelled UA does MHT->EWR first. I've definitely driven from EWR to MHT several times at 2AM due to delayed/cancelled flights.