Which manufacturer makes the best air conditioner?

I hesitate to recommend one brand over another so here are a couple of general guidelines.

Air conditioning is a matured technology so almost all the popular brands work equally well. Most of them use parts made by the same manufacturers. The main considerations then would be the price, warranty, attractiveness, noise, etc.

Some manufacturers offer a 5 year warranty on all parts while others offer only 1 year.
Some offer 10 years on the compressor while some offer only 5 years. Some units are straight out ugly and will be of no compliment to your landscaping.

Whatever you decide, by far the most important consideration is the contractor you use. You may buy the best system in the world but if it is not properly installed, you will actually be buying nothing but a big headache for years to come.

And, don't forget! Dirt is the biggest enemy of your air conditioner, and a good air filter is the best friend! Giving your air conditioning system an efficient, high MERV rating air filter is the best thing you can do for your air conditioner. A good air filter will extend the life of your air conditioner because the important parts, like the blower assembly, the cooling coil, and other inner parts will stay cleaner, operate more efficiently and last longer.

And, as a side benefit of having a good air filter, your family and you will enjoy breathing much healthier indoor air. Air that will be free of dustmites, mold, mildew, dust, pet dander, etc. etc.