In either scenario the Bills still have a lot to do to get to the playoffs so everyone should understand that this is just in theory.
Once you accept that, the choice is still difficult until you look at the schedule. If they lose to the Pats and then beat the Bengals and Eagles they will have put themselves in a bad tie-breaker scenario because the sequence of importance is:
Division game
Conference game
Non-conference game.
The NE loss hurts the Bills in a tie breaker as would the win against the Eagles. The Bengals game is more of a neutral. Based on this the obvious choice if you want the Bills to make the playoffs is take the win against NE. At the end of the season there might be a lot of ties this year. I can see the Pats, Jets, Bills, Ravens, Steelers, Browns, Texans, Chargers, Raiders, and possibly the Titans in the playoff mix. That is 10 teams for 6 spots. That means you want the best tie breaker scenario possible which means:
GO BILLS!!!!!!!!!!. BEAT THE PATS!!!!!!!!!!!!