The short answer is: buy the largest you have space for and most expensive one you're willing to spend. Air compressor is one of those things that once you have one, you'll start to come up with more and more uses for it. And the SCFM you might want/need will increase more and more.Any recommendations for an air compressor? I do not own onecurrently.
I started out with a Sears 1HP 2gal oil-less long time ago. Did a whole lot of stuff with it. Even painted an entire VW GTI. But that was really really pushing it.
When I bought my own home and finally had my own garage, air compressor upgrade was a must. Went with a 3.0HP 20gal Cambell Hausfeld, which I thought would be plenty. Well... for a while yes. Then I started running air tools that were just SCFM hogs, and that poor compressor struggled to keep up and was running continuously at time. Not good for long service life.
Then I happened on a Husky 7.5HP 80gal dual stage that Home Depot was clearancing out. I've been happy since.
That said, unless you have access to 220VAC, or know how to add a circuit, you'll be limited on HP on 110VAC. In that case, go with a largest tank you can find that still runs on 110VAC. That will help reduce the ON duty cycle. Vertical tanks are your best bet for not tying up a lot of garage space.