I have 2000 Sq feet home , I have original 30+ furnace that has 65K btu input and 49K btu output, and 2 Ton A/C., I had load calculation done and min BTU recommended for my home and size and the location is 70 K btu , was told this furnace is small for my house and the motor is not strong enough to push enough air up, the piping going to each rooms upstairs is 10in in diameter
issue I have with old furnace was not heating enough to upper floors and not cooling enough during summer I had to crank up heat or lower to cool down so enough get up stairs, I have set register in basement to try to push more heat/cool up but I am running to issues where those area are not properly regulated

so I have 3 contractors coming offering different option
1 contractor
offer to replace with the same size furnace 2 stage 70K btu
1 stage is 43k in / 41 out 2nd stage is 66k in and 62 out
2 ton A/C

2 contractor
offer 2 stage 90K btu 1stage 57in/55out 2stage 88in/84out
and 3 ton unit

3 contractor
offer 2 stage 110k BTu 1 stage 72in/70out and 2stage 110in/105out
and 4 ton unit

now I have dillema based on the load I had done which one I should go
each of them had their own reasons for choosing this unit and what is available on the market I am going with Ducane or Lennox depends by contractor offer
the first contractor dismissed the report and says I should choose identical unit size if I go higher BTU i might have issues and I got entire lesson but it would fill two pages, the second said that I will have two stage furnace if need more heat it will go to stage two and this is what he recommends
the third one said that going by the load calculation done on my house that the furnace will work much better it delivers the min but if more heat needed it will go to next stage if needed be .. looking for suggestions on this I thought it will be easier to made decision but my head spins , or should I try couple more