I had meant that line as a joke, just because everyone's answer would be influenced by what canons they know. I haven't read Discworld or Young Wizards (right?) (or A Wrinkle in Time, actually), so they just don't mean much to me. Wasn't necessarily criticizing your picks, but since you asked:
I also haven't watched Back to the Future all the way through—long movie is long, and doctorlit gets antsy from sitting still too long. But I would still pick Doc Brown, if only because Morgan seems to be a fan, and irony is tasty. Plus, his continuum and Doctor Who seem to take similarly chaotic, sci-fi views towards time travel (from what little I've seen of both shows), so he would have a fair idea of what's going on.
I would definitely have to pick Teferi from MAgic: the Gathering. This is a man who not only survived major temporal trauma (being trapped in a slow time bubble mid explosion, and basically performing a single dive through flames to escape a burning room over a span of decades), but also fought against other planeswalkers (super-wizards) to stop their little conflicts from enveloping entire worlds. He's also a powerful time mage himself, putting his own country out of "phase" with the rest of the planet to let it escape a global war. Finally, he sealed off a series of time rifts that were threatening to destabilize (the same) world. I think he's quite equipped to battle Time Lords!
For number three, a bit of cheating: the Ellimist and Crayak, both from Animorphs. They're both beings with the power to basically create and change entire timelines at will, with a mind to making the universe the way they want it to be. Neither would appreciate such a massive level of outside interference. While they're normally enemies, I can imagine a team-up pretty easily; the Ellimist would go to far lengths to put his continuum back the way it should, and Crayak would want to continue his universe-size chess game unmolested. (And, as a villain, he would be majorly targeted by the Continuity Council to begin with.)
Lastly, well—I really like your use of Jareth, actually? He's not a charcter you would regularly associate with the concept of time, but when you think about how he can manipulate the Labyrinth, and people's minds, it's actually pretty clear he does wield some control over it. Some might argue that his powers wouldn't work outside the Labyrinth, but you have to consider: Sarah's parents seem to be out to dinner an awfully long time, don't you think? (I forget what they were doing, but whatever it was: dinner, movie, show, they shouldn't have been gone that long.)
So, yeah. Again, it's just a familiarity thing, and I wound up ripping off half your list anyway.
