Hi Bob: Check out the January 98 issue of Fine Homebuilding. There is a good basic review and spec sheets on 24 of the portable compressors available, written by Jim Britton. Jim provides a basic primer on the difference between oil bath vs no-oil bath types, the importance of good air filters and several good tips and guides. Unfortunately, this is not a Consumer Reports style review. With the exception of measuring recovery times (in seconds), the article doesn't provide much objective data. It is definitely worth reading if you are considering buying a new compressor.
FWIW, the unit he personally uses is the 1.5 hp Campbell-Hausfield twin tank oil-less. I guess I'm old fashioned, but I like the oil-baths, but then I always do maintenance on my hardware. IMO, checking and maintaining the air filter, draining the tank and changing the oil should be SOP.