Why not try both? A tunable loop isn't hard to build. All you need is a plastic milk crate (roughly 30cm square -- that's the size they sell in the US box stores), 33 meters of wire (roughly -- 110 feet in US measurements is what I used to build mine) and a 365 pf variable tuner capacitor. Some tape, a few zip ties to hold the tuner to the crate, and two alligator clips. With my crate loop I've heard stations from 2000 miles away or more (3000 km?).
I don't know what antenna connector the ATS 20+ has, but if it doesn't have a loopstick, I think you'd have to use a sense loop to couple the crate loop to the radio.
If you have a tuner cap, it would be worth trying.
As for outdoor wire antennas, I'm not sure what would be best for MW, when it comes to choosing a loop over a regular long wire. I think with MW, the longer the better. You don't really get a lot of directionality with a MW wire until you reach half wave, which is around 250m if you're trying to get the lower end of the MW band. 250m is impractical for a lot of DXers, because we don't have that much territory. I had a 150 foot low wire and was able to DX the MW band with it in 2011-2012. I think 150 ft is around 50 meters? I heard Mexican stations 1500 miles away (2000 km or so) or more with that wire.