We had Houk A/C come out and install Trane HVAC system back in August. Outside unit is a XL 19i, inside XV80. The dual compressor unit cut the the utility bill significantly. This unit covers approx 2600 sq ft. with two thermostats and electronically controlled dampners. The seer rating was 17 I think. It is a very quiet unit. We were very pleased with the installers, and the service the unit provides.
I would look into getting a Trane.
It replaced a 20 year old carrier unit. Not sure whether the carrier product today is what it was then.
Here's a starting point for you.
http://www.trane.com/Residential/Products/AirConditioners/XL19i.aspx
We bought the 4 ton unit.
No relations with the aforementioned company, just a happy consumer.