I'm not far from you (central Bucks). In our climate, factoring in all things (like expected future elec rate hikes, very unknown future fossil fuel prices etc) my opinion is a heat pump with fossil fuel back up on 1st floor is optimum. Regarding 2nd floor, typically I'll go heat pump with elec back up....since some of your 1st floor heat will make it's way upstairs, the 2nd floor back up (assuming good attic insulation etc) should require relatively little useage. Note also, this approach serves to diversify your energy demands. In some years it may prove imperfect, in years of $4+/gal oil, you'll be thankful.
Also, as you noted, the best bang for the buck is KEEPING the conditioned air (either heated or cooled) that you pay to make. That means proper air sealing/insulation, etc etc. I've seen (and fixed) attic insulation that was insufficient in quality and/or quantity.
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