Look at the CFM rating of the most air hungry tool you'll be using. Get a compressor that has a higher rating than that in 'continuous' mode. As a rule the smaller, mobile compressors are only good for airing up tires. You'll be far happier in the long run to buy a stationary unit then run line drops to various places around your shop/garage. I bought an IR 80 gal capable of 18.2 CFM @ 90 PSI then ran pipe around the shop with several drops, all regulated. I have one full pressure drop just off of the compressor. I'm happy as a pig in ^*%#$ with my setup.

Save a life, adopt a senior shelter pet.
The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.