Which Air Compressor should I buy?

It depends on what you want to do with it. If you want to run air tools and such, I would go at least 5 HP, two stage and larger tank, minimum 50 gal.

I have a single stage 5 HP 30 gallon and it won't keep up with my air tools, it will run them for short bursts then I have to wait, that is MOST frustrating.

If you want portable, I would suggest something in the smaller category and then something larger for your garage.

I know it's an expense but IF you can afford to, I would do it right the first time.