If they ever fought, I'd certainly root for Mousasi. But the correct answer here is Luke.
1. Luke was UFC champion. And he wasn't gifted a title shot. He earned the shot and won decisively.
2. Losses should also be factored in. In the last few years, Mousasi has 3 losses and Luke has 2. Luke has one terrible loss - against Bisping. But Mousasi's loss to Hall is worse. And he got outclassed by both Jacare and Lyoto. Luke got KO'd by TRTVitor, but who didn't?
3. TS listed a bunch of questionable fights as "wins." How many ranked opponents did Mousasi beat? Most of the guys on his list were either very pre-prime, very past-prime, or simply journeymen. You might be able to make a similar argument for Luke, but he clearly has the most notable win (smashing prime Weidman).