I am looking to replace my current York central AC system and I could use some advice on a new system. I have had a number of installers come out to give estimates, most recommending the Rheeme 13 seer unit. In addition, I had Sears come out for and estimate and they really pushed the 15 seer Carrier Performance unit with variable speed air handler. The overall price was about $1500 more but I just assumed that was due to the fact that it was Sears and that the unit had a higher Seer rating. Money aside, what brands and features should I be looking at to replace my existing 3.5 ton York unit? How does Carrier rate in comparison with some of the other common systems, Rheeme, Trane, York, Comfortmaker?