AC units, at least those made in the USA are nearly the same. Each manufacturer buy parts from all sources and do mainly the finally assembly. Many use generic controllers and thermostats. Almost all use the Copeland Scroll compressor, however I read some rumblings there is one brand that switched to an LG scroll compressor and it is having problems. I do not remember the brand. Where the brands differentiate is usually the high SEER rated models where they design the control boards (computer based) with proprietary thermostats. If you look at Carrier, it is identical to Bryant, Goodman, Lennox, Trane, Rheem are all about the same quality. The design and quality will vary on the compressor housings and the air handlers will barley have any differences. I have a carrier and the cheap part of it is the compressor housing. The side are open with a little wire mesh for protection. The advantage of it is rain will keep the coils clean from dust accumulation. Most have gone to powered coated housing grills that look good and protects the coils from mower and kid damage, but you need to open it once in awhile to flush the coils down of dirt and dust.
As LKbros mentioned, the most important part is service and support from your local dealer.