What matters more — is the compressor a single stage or a two stage, or who built it? In almost every case, the manufacturer matters more than the stage count. An industrial-grade piston compressor from Atlas Copco, Ingersoll Rand, or Quincy will out-perform and out-last a cheap brand's two-stage unit. Every time.

Don't get sold on stages. Get sold on the company that's going to have your back when something breaks.

Horsepower — the number to ignore

Horsepower or engine power (in HP or kW) is not really important. It's just something that follows naturally given the pressure and capacity of the compressor. For X amount of capacity/air flow at Y pressure, we need a certain amount of power. It's all physics, cannot change it. Since we know the pressure and capacity we need, horsepower is not really important. Besides, lot's of manufacturers will 'exaggerate' (or you can say ' lie' ) the horsepower of the machine. This is especially true for the smaller piston type compressors.

Most people think bigger = better. Lot's of brands and shops will use terms like 'peak horse power', which is technically a wrong term. When a compressor (or any machine) starts up, it draws 3 - 7 times the normal electrical power, but for only a few seconds. Some brands take this 'peak' current and calculate it into their 'peak horse power', which is completely nonsense!

Where are they made?

I know people value the 'made in the USA' air compressors. While I can understand this, it's not as simple as that. A compressors consists of many, many different parts. With most air compressors, at least some parts are from China or India. Secondly, some air compressors are 'Assembled in the USA', but the individual parts are imported from other countries. This doesn't necessarily means it's low quality, just the manufacturer is trying to trick you :)

Here is what I was able to find out:

Quincy

Pump, motor and tank are made in the USA.

Ingersoll Rand

Ingersoll Rand single/double stage air compressors are 'assembled in the United States'. But, the individual parts come from other countires: The pump is made in China or India. The electrical motor is made in from Mexico

Campbell Hausfeld

If the pump has 'made in the usa' cast into it, it is made in the USA. If not, it is imported from China or Inda. I am not sure about the motor and tank.

Husky

Husky compressors are the same as Campbell Hausfeld.

Atlas Copco

Atlas Copco compressors are either made in Belgium or Italy.

Electrical supply matters too

Since two stage are compressors are a lot bigger than single stage air compressor, the right electrical connection becomes important. Make sure that you have an adequate power supply available at the place where you want to install your compressor. Have it installed by an electrician when necessary.

Some compressors can be bought either with a single fase or 3-phase motor. And often you can choose between 200 volts, 230 volts or 460 volts. Make sure you choose the correct type for your situation.

Bigger two stage compressors only come as 3-phase machines. Keep in mind that most dual stage air compressors come without any wiring, so you have supply that too.