other than improved efficiencies which translates to lower operating costs, the Fed Govt is actually paying you to upgrade to take advantage of the Fed Govt HVAC tax credit.

these are my minimum specs for a new HP system. both outside and inside units should be replaced to have a properly matched system.

15 SEER, 12.5+ EER, 9 HSPF
best matching VS air handler
full BTUs in both cooling and heating for your rated size
R-410a refrigerant(same as Puron)
scroll compressor preferred
electronic demand defrost preferred
thermostat with "dehumidify on demand" feature
staged backup heat strips
new and correctly sized refrigerant lineset

you want a thorough inspection of your ductwork system. size, overall condition, supply and return lines, insulation qualities, leak test, etc.

any hot/cold spot issues in your home should be addressed.

I would only use authorized dealers for the various brands that provide quotes. see mfg websites.

I would look at Trane/AmStd,Rheem,Carrier/Bryant.

IMO

There are a few web sites that will price it out for you. FPL had a good one. Also, I think the University of Florida has one too. Just punch in the numbers and it will get you an idea of savings.

15 SEER, 12.5+ EER, 9 HSPF
this is a good deal.
instead of legal minimum (13 SEER) this upgrade
will give you a much better performance
& comfort level.
this is what I recommend to my clients.

best of luck

You can option demand defrost on the outside unit and a txv valve on the indoor coil which are musts in my book if you want comfort along with efficiency and on a 13 seer you will be in range of opting to a 15 seer that usually has these options standard for a little more money.