For my one and absolute favorite, as much as I would like to say Batman TAS, it would be Batman Beyond for me.
Batman TAS was what paved the way for all modern DC cartoons today, it created a show that could be dark, hold mature themes, and still be directed at a younger audience. It is essentially the pinnacle of all DC cartoons, until season 4, that is.
But Batman Beyond took what Batman TAS stood for, and just built it on from there. It wasn't as dark, we got a punk kid who was forged by tragedy, but that doesn't prevent him from getting happiness. We get to see Terry grow as a person and as a batman, proving that he does not have to be the same as Bruce to keep up the mantle (and he isn't). The show has some themes which are just as dark, if not darker, than the original (Terry's actions do sometimes lead to peoples' deaths, the fate of Mr. Freeze, the venom episode which shows the fate of Bane, or the entire Return of the Joker movie), while throwing pop culture and other references (like the fantastic 4 homage episode).
Superman was a great show, just not my favorite.
Static Shock was good for what it was and introduced me to my all-time favorite DC character, Static. His comics were great as well as the character.
JL and JLU were pretty great and pretty much combined the themes of Batman TAS and Superman TAS with a few other ideas, making a perfect mix. Just not as good as Batman Beyond, though.
Teen Titans was great and was even my favorite as a kid, but the only thing keeping it from being my favorite was Batman Beyond. At times, they have some similar themes and ideas and the show has an amazing cast that feels real. Teen Titans is the definitive superhero team show, even better than JL/JLU.
Young Justice was pretty great and had an even greater potential. It didn't go as far as it set itself up without meeting its own goals. The drama and inter-team dating was okay, but really hindered the show. Overall, it was a rushed series, likely due to cartoon network being stupid.
Young Justice does get a positive rating from me because it saved Static, who was almost killed off by the New 52's awful writing and producers trying to take over the writer's job.