Couple of weeks ago, I was bored. I set myself up at a pinch point near the Southwest gates and did a little survey. As quickly as I could, I noted the luggage choices of roughly 150 travelers in five minutes. I ignored families with kiddies because I did not have a column on my survey form for stuffed animals.
18 No luggage (presumed checked bags or just carefree)
62 Spinner with shoulder bag, small backpack, or no personal item
35 Spinner with sleeved personal item (often a matched set)
22 Wheelie with shoulder bag, small backpack, or no personal item
12 Wheelie with sleeved personal item (often a matched set)
14 Backpack (travel-specific or hiking style) with or without personal item
By far, the most popular choice these days is a spinner.
I had a chance to chat with a few backpack users and we agreed it was the best carry-on option but they could also see moving to a spinner with their next luggage purchase.