Based on the information you've provided, sounds like the York quote is the best option, but I don't agree with the 80% modulating furnace. That's a high-end furnace, and going with the 80% version doesn't make sense to me, especially in our region where it can get cold at times (I'm in Maryland). Is PVC venting an issue? The York Affinity is a nice line of equipment. American Standard isn't bad, either, but the equipment that the York rep. is quoting is better in my opinion. 3 tons is a bit much for your cooling load, but it's what you'd have to go with if you went with the Affinity line. The 2.5-ton Latitude unit would be the better fit. With the low stage on the Affinity approximately meeting the cooling load at design conditions (which won't be met on all days), I don't think you'll be getting those long run times that you should with a 2-stage system. Ask the York rep. if he can quote the CZB or YZB 2.5-ton single-stage Affinity unit with a 90+ efficient v/s furnace (modulating or 2-stage). Not sure where the American Standard rep. came up with his sizing. Do you like it cold in your house (68-70)? Did the York rep. do the load calculation?

Where milder/less mild matters is in the heating season with a heat pump. The AC functions about the same, but if it's too cold out the heat pump BTU output may not be enough to keep up. Even if you have plenty of AC capacity in the summer. I assume you're on NG and not propane. Also, $2.1 per hundred cubic feet (ccf) would be more normal. Ours in ATL is around $1/therm (therm = ccf), and it might be $2.1 once you add on the administrative costs. It might make sense, if you're already paying the overhead on your NG account, to go with a dual fuel system. The extra use spreads that admin cost further, if your system is set up to do it when it makes sense. A dual fuel system will run the HP until it can't keep up (or the controls lock it out based on outside temperature), then kick on the gas furnace as the 2nd stage. This takes advantage of running the heat pump most of the time without needing electric heating strips as backup heat. The HP will put out about 3X as much heat as the energy it uses- that's what makes it cheaper to run than a NG furnace. But the backup heat strips are 1:1 on energy to heat, which usually isn't competitive with NG. Also, I kind of like the idea of having a standard efficiency gas water heater. Offends my drive for efficiency, but as a kid on the N end of AL, the power went out enough during hurricanes, ice storms and the like that it was nice to still have hot water (and a fireplace) when that stuff happened.

It depends on where you are located geographically. I have what is called a dual fuel system--heat pump and natural gas. My heatng bills are about the lowest in my subdivision of 64 custom homes (the gentleman with radiant floor heat and two other guys that burn wood pay a little less). Folks in our subdivision that use natural gas furnaces only have much higher bills than mine. Folks that don't set their heat pump balance points have heating bills higher than mine. I set mine so the natural gas furnace doesn't kick on until about 25 degrees outside. I am well insulated with great windows, energy efficient and have a 3.5 tone HP for 2,981 sq. ft. 1.5 stories. Depends on your home envelope, too. Check your electric and natural gas rates which includes delivered price (i.e. total cost you paid for electricity including service charges divided by total KWH and total cost for gas including service charges divided by total therms or Cubic feet used to get your real world costs. In my case, natural gas needs to come down about 35 cents delivered price before it breaks even with my electric. Your rates will likely vary.

Gas heater PROS heats very fast less money upfront CONS very expensive to operate heat exchanger will corrode if pool chemistry is off Heat pump PROS Inexpensive to run(u spend $1 heating pool and get $5 in return) titanium heat exchanger will not corrode uses the humidity and heat in the air to heat your pool keeps pool temp steady on u reach desired temp CONS high inicial/upfront cost( around $2500 to $4500) slow inicial heating(takes days) all in all heat pump is the way to go as far as i am concerned its the only way to go(gas vs heat pump) hope this helps