delima... advice needed Hvac

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I have a big decision to make this monday.
I have a 6000 squart ft home that is wide open with 24 ft ceilings and a lot of galss.
We just moved in about two weeks ago and knew going into it that we would have to replace the Hvac system that is in here now. It has a total 35 year old, 10 tons of electric heat and air. Meanless to say extremly expensive to run. I have two bids... one a waterfurnace with a total of 12 tons and a dual fuel system with propane back-up. My goal (like everyone else) is to chop utilities way down and also do a better job of making it comfortable during our hot summers and cold winters.
I want some opinions! Not neccasarily on size of units but on whick one will most likely help me acheive my 2 goals.
So let me have it!
Thanks
Phogan