I was you at this time last year. Here's what I learned:
The cheap Quincy & IR units seem to be a little on the flimsy side; I would steer clear of them, especially the IR. I would suggest you look for a compressor with the following features, in descending order of importance:
Low pump speed
Cast-iron pump
Disk valves (not reed valves)
Two-stage
Pressure-lubricated (Important in industrial settings, but home gamers can usually cut this corner and be fine).
In air compressors as in most things, you pretty much get what you pay for.
I looked at high-end Quincy units ($$$$$) Saylor-Beall units ($$$$$), VMAC portable compressors($$$$$) and Rolair ($$). I was contemplating cheaping out and getting a Rolair or saving up for the best Saylor-Beall I could dream of when I found an '80s Curtis "Master" line 5hp 80 gallon with a recently replaced pump for $800.
5hp is barely enough for me, running die grinders, lots of plasma cutting, 1/2" and 3/4" impact wrenches, a 9" 5HP air angle grinder (intermittently

), and a big Cleco air drill. I never use more than one tool at a time and never have to wait on the compressor unless I'm using the big grinder.
If you have a few months to diligently check FB and CL every day or two and are willing to travel a bit, you just might score a good deal. Otherwise, if you want a quality product in a hurry you will have to pay for it. Even at a Rolair price point, even a cheap compressor can last a while if decently built and treated well.
Finally, there are ways to make the most of whatever compressor you have. I had to learn these from harsh experience, hopefully they are some help:
1) Friction in your air delivery system is the enemy. It saps your air pressure when you most need it and wastes valuable power.
2) Throw your 3/8" air hoses and 1/4" quick-connect fittings in the trash and never look back. I use 1/2" industrial quick-connect fittings and consider them just about adequate. One warning though:
They are much harder to connect than 1/4" fittings and, just like a 1/4" fitting if not connected completely can pop loose and maybe injure you when you let go.
3) If you build an air supply system, use 1" pipe minimum, from the compressor tank all the way to the attachment point for the air hose
4) If your compressor doesn't have a magnetic starter, install one. I had a pressure switch stick closed and ran the pressure up to 180 PSI because I foolishly tried to have it switch the motor directly.
5) It will cost more than you think, but will be worth every penny in the end
