Here in NW FL...
We sell American Standard... I know people will be commenting "to pricey!". I actually just re-did my home A/C also with what we sell. Honestly, I am extremely pleased by my new system. I have an 18 SEER dual compressor, variable speed. We did pay more for the better system, but with utility prices on a rise, it will pay off SOON!
The way the dual compressor works, is the smaller compressor runs most of the time unless the demand for cool is very high (people coming and going all the time, group gatherings... )then the bigger compressor turns on. **less power usuage
The variable speed is good too. It takes a lot of power just to start a unit, but with variable speed, the blower starts slow and ramps up (makes airflow quieter and doesn't have power on with such high start power *which saves with power used just to start). Also, w/variable speed the blower doesn't always have to run at one speed, if it doesn't need to run at highspeed it won't... it will run at a lower speed (using less power). We added the American Std. Accuclean airfilter to our air handler. That's a great addition too! The thing is, in order for it to filter to is greatest extent you need to run your blower constantly (to clean the air constantly! ) with variable spd. You can run you blower all day long and it cost about 5cents a day to contantly clean the air.
Think about this too... turning a light bulb on and off constantly is what makes it burn out faster, it's the same concept with electrical motors. (its the constant on and off that wears them out faster... not them running
Keep in mind, the initial investment may be high for good efficiency equipment, but the cost of living will be lower!!
Talk to different consultants and see what will fit YOUR needs! After you've done your research take a look at HVAC OpCost
and just plug in your equipment info and it will help put some of the investment cost into a longer view of cost difference! GREAT WEBSITE for ballpark ranges! (Granted it won't be exact... but it does a good job of breaking it down)