A heat pump should fit the house it serves, not the unit it replaces. The questions that matter are about how your household uses the heat, how the building holds that heat, and whether the site and the ductwork can take the new equipment. Work through them in this order before anyone quotes a model.
Start with the heating pattern in your house
Write down when the house is occupied, which rooms are heated in the cold months, and whether any rooms stay closed for long stretches. A house that is heated steadily in a few zones fits differently from one that is heated in short bursts across every room. Give that pattern to the installer before equipment is discussed.
Ask for the heat load, not the old unit size
Ask how the heat load was worked out. Replacing the old equipment with the same size is a shortcut, not a calculation. Ask whether the calculation accounts for insulation, air leakage, window area, and any rooms that were finished or added after the original install. Ask which design temperature the calculation uses for your area, and whether the installer can explain how that temperature was chosen.
Look at the outdoor unit site
Walk the outdoor site with the installer. Check the clearance the manufacturer's manual calls for on each side and above the unit. Check the pad, the level, the drainage, and the snow line in your area. Check the distance to bedroom windows and to the property line. Ask where the condensate will drain during the coldest weeks.
Look at the indoor air handler and the ducts
Find the place the indoor unit will sit, and check whether the closet or room gives the service clearance it needs. Check the return path and the filter size. Ask whether the existing ducts were sized for the new airflow or whether the installer plans to test them. A duct run that suited the old unit may not suit the new one.
Ask how it will heat in the coldest weeks
Ask how the system performs at the design temperature, what the backup heat is, and when it engages. Ask how the thermostat moves between heat pump and backup modes. Ask what the installer will check to confirm the controls match the way your household runs the house.
Place the unit on the planning calendar
The Heat Pump: typical service life and when to plan page on this site lists the typical service life and shows how to turn the install year into a planning date. Add that date to the same calendar where you track the furnace or boiler, so the next decision arrives on a schedule rather than in the middle of a cold week.