Let's say that the TSA120 scores as a 100 visually. The SW120ED would probably be approx. an 85, in comparison. Boy, I am really opening myself up to being lambasted with this.
I have owned both. In fact, I have owned a couple of each over the past eight or nine years.
I would say that might be a fair comparison -- if you are talking about the Original version of the SW 120ED. You know, the one that actually used FPL-53 and Schott glass. That particular scope was one of the best deals in astronomy. Outstanding optics in a bargain tube. Spend a few extra bucks to upgrade that cheap, "beginner's scope" focuser and you could have a world-class telescope without breaking the bank.
But times change.
Now I have no idea if the SW 120ED that has been sold since early 2019 is as good as their original versions. Sky-Watcher changed the glass formulas when they brought out the SW-150 and they will no longer disclose what glass they are using in their ED refractors anymore.
Our problem as consumers is that retailers around the world are still using the exact same marketing blurbs from the original production of these scopes that tout FPL-53 and Schott BK-7. But when you receive your SW 120ED (if you go that route), you will notice that the Schott brand is no longer on the OTA where it was originally located and you don't have a clue as to what they are using.
If you don't care about the glass or the bargain focuser, then spending 50 percent of the cost for a TSA-120 might bring you a lot of joy and happiness. But if you are used to decent optics, the Tak is a sure thing.