Which would be better fit for a boost test?

Campbell Hausfeld 3 Gallon Air Compressor Kit 100PSI | eBay

Campbell Hausfeld 1 gallon Pancake Air Compressor | eBay

 

If you're in Chicago as your profile suggests there should be a Harbor Freight store within about 30mins from you. Their stuff, while cheap, generally works well enough.

Air Compressors & Air Compressor Accessories

You don't need much of an air compressor for a boost leak test, since normally you don't need to test above 10psi. So unless you have another need for an air compressor you can get something less expensive. Although 3gal. minimum might be ideal (for general use).