I supply within the industry and there are many difference on the various suppliers. Virtually all the compressors with 30 gallon above tanks are assembled in the states, basically due to the tank size, it is not functional due to the shipping cost from Asia. (asia is loosing placement in many locations). Quincy and Champion have two major advantages, they machine their compressors in house on equipment that is better than many of our engines were machined on. Champion, which is a Gardner Denver company as well as Quicny, a Atlas Copco company, have great equipment, with Champion mabey having more cnc. I would put them at a tie in quality and just rate the machine cfm you want. There is no other oem supplier that has their standards in place. Curtis is doing less and less domestic since the Asian parent took over. All the electric motors are sourced but the tanks come from one of two USA suppliers. Valves are all made in the states for compressors basically due to ASME/CE requirements. IR pumps were made in KY but now made in India, which are a great pump. I saw a note above about BelAir, made in NC with supplied pump but it is an excellent facility, also related to Copco. Campbell is getting back up in quality but still behind, forget what part of the world their bigger pumps come from, believe its China. From what you are targeting, Quincy or champion, you might as well plan on who you will leave it too as it will last for ever. Heavier than shit, but top of the line. Small rotary units are another topic. I have a TS5 pump on my IR 80 gallon, love it, also have a beater Ridgid in my trailer. Most of the Lowes, China Depot, and Sear units are assembled in the states, its a matter of finding which ones are as the plants are making the best quality they can as they are really trying to move business back into the states, and winning. If you want a great small compressor, the depot pancakes for Dewalt are assembled to tight standards, in Tennesse.