I am in the market for a larger air compressor.

I try to buy good used equipment. I am leaning towards Champion and IR
for the two brands that I like...if you have other suggestions I would
to like to hear them.

When I look through the Usenet archives, I find repeated references to
how older compressors and their compressors were built better.

Well, are they?

Is it better to buy a new unit today that is likely value engineered
versus searching for a 20+ year old compressor like a Champion or an IR
T30 series?

The next question is what should one look for in an used air
compressor? What do you look at to size up whether an air compressor is
a buy or a dog?

I would guess that any compressor that I will want would likely be 3PH.
How would you recommend running a 2-5HP 3PH compressor in a shop with a
100 amp single phase panel? Rotary converter, VFD or replace the
compressor motor?

Finally, what do you consider to be a fair price for an used compressor
like a IR T30 5hp 80 gallon or a Champion 3hp 60 gallon that is 20
years or older? What percentage of the new price of a comparable
compressor would it be?

Thanks for all you can offer.

TMT