Thought of this when I saw the Batman one a while back. Is it X-Men: The Animated Series, X--Men: Evolution, Wolverine and Tehe X-Men or some thother showfeaturin everyone's mutants? Mine is X-Men: The Animated Series by default. To me, this is the definite on-screen X-Men which not only introdouced me to these astonishing chrracters and the world they live in, but the also stories were Calremontish. All the chracters had enough spotlight as well. Voices were mostly good. The only flaws to me were some of the dialogue and animation. Evolution was too much like Dawson's Creek and Smallville in the first couple of seasons and then it got better by season 3. So, I rank it second. Wolverine and X-Men was underwhelming due to it being cut short.
The old X-Men show from the '90s has bored me to tears watching it all over again, save an episode or two per season. I enjoyed the Wolverine and the X-men series late last year watching the DVDs. I wish they could have done Season 2 as they planned.
Wolverine & the X-Men. While the first two seasons of FoX-Men were good, after that the series went downhill, and it became less about "storyline" and more about "one-shot episodes" and "guest character of the ep". No continuity, no sense of "zomg" ... just one-shot episodes. X-Men Evolution was a joke until the end. It was silly, cartoonish, and didn't develop until the show was practically over. Wolverine & the X-Men was a step in the right direction, but the X-Men draw just isn't there right now. Cartoons in general are on the decline.
The only new awesome cartoons I could think of these days are Genndy Tatorsky's Symbionic Titan ( which got canned a couple of weeks ago) and the Avengers series.
The only reason I can't say this is my favorite is because of it's "ending". I understand why series get canceled, but sometimes I'd rather not watch something at all, than watch something that ends in such a big cliffhanger.