I didn't read the other responses, but here's my thoughts. I have two criteria, how many passes do I have to make, and can I move this thing around to places where I have to move it. In and out of the garage and such.
A lot of what I do is sidewalk, so I make 2 passes, one going down, one coming back. So the sidewalk is 36 inches or so, so no matter what machine I had, I'd still have to walk down and back. So the 24 inch is plenty.
My driveway is 25 feet wide. That's 12 passes with a 24 inch. A 28 inch is 11 passes, hardly a difference. A 32 is 10 passes. a 36 is 9 passes.
So the question is, is it worth 3 passes on the driveway to have to deal with a 36 inch monster? I can barely get the 24 inch in and out of the garage behind the cars, into the shed, etc... It's just a monster to move around where I'm at. Now, if I had one of those beautiful shops some others around the country have, like the 30x50 shops, it wouldn't be a problem, my shed is 14x12 with two 30 inch doors that open from the middle.
At my dad's house, he has a narrow sidewalk around the side that we use an Airens 20 inch on , because any bigger is a hassle.
I live in a place where the homes are on 75x100 lots, so it's not all that much real estate to do, so the 24 is fine for me.
if I had more to do, I may have gone bigger.