Depends upon the size of your garage, and what you want to do. You can run a 1/2" impact off anything with a regulator. It depends upon how much you want to do without waiting for it to re-pressurize.
My dad's shop/garage, we have a 60 gallon with a 5hp motor. No waiting. I can sandblast parts and it can keep up. Run air tools including a 1/2" impact, snap on a hose to blow off the concrete pad, pretty much use it all day.
Brand is honestly not that important as a) quality of your fittings downstream to not leak matter, and b) Motor on different brands changes year to year it seems to me.
I love to sandblast and refinish stuff; to me that is the best use of an air compressor. Impact, when I need it, I can substitute a hammer unit or a large lever to get the job done. Not the most important use of an air compressor to me. Thus, I love the 60 gallon and 5hp set up. Once you have that, you will be surprised how cheap cabinets are and the new things you can do. The marginal cost on slightly larger compressor tanks vs. 20 and 30, and motors, can be small. So don't go too small, if you have the space, is my opinion.