Shop with a tape measure!

There are several companies including COSTCO selling so-called 22 inch carry on bags that are actually 23.5 inches long. You have to include the handle in the measurement.

It is impossible to predict what surprises the various airlines have in store for us. If you are in mind to only own one bag, then I would go for the 20 inch bag.

That said I gave up using a wheeled bag a couple years ago and have been very happy since with no regrets. The weight of a wheeled bag is something I resent. The immediate weight savings I had going to a RedOxx non-wheeled bag was over 5 pounds.