Okay, I need some info. Is the Raven backstory the same for the cartoon as for the comics? Because there’s an awful lot of exculpatory circumstance behind Raven’s behavior if it is…
In the broad strokes, anyway, if not the details. We meet Trigon (or at least Raven’s mental imaging of the side of her that comes from him) at the end of Nevermore.
Now, Raven is my favourite character in the show (followed closely by BB). But she (nor he, really) isn’t leader material. Between the danger that she is when she loses the grip on her demonic side, and her secrecy - the rather extreme situations in Switched and Nevermore are the only times she reveals ANYTHING about herself - it’s very hard for the rest of the team to trust her. And, has been said, she doesn’t step up to take the lead at any point where she could, and the few times she does, she’s ignored - because it’s mostly ‘leave this to me’ when the others see (rightly or wrongly) she’s outmatched. (The one example of possible GOOD leadership skills I can think of is when she pulled Cy out of his mope after the T-car was stolen.) Even if she had any intention of being a leader, nobody would follow.
As to who would be leader if not Robin? They’d really need to introduce another character. None of them really work.
Starfire’s an impulsive flake.
Raven’s…well, look up.
Beast Boy’s a goof.
Cy’s the best bet, but he’s a bit of a hothead, and more tech-smart than anything else. He’s also the most prone to giving up when it gets tough.
Looking at the times when Robin has been taken out of the picture, Starfire’s the one who’s stepped up into a semi-leadership position - or, rather a ‘move your ass, we have to do something’ position.
Raven’s smart (I disagree that she’s smarter than Robin, or even Cy, though.), but she’s not a leader. She’s overconfident about her skills, but insecure about her relationship to others, so she tries to go it alone if left with the option - often with bad results, especially since she’s also got that demonic side that pops up every so often.
OK, I’m repeating myself here, so I guess I’ve said enough.
Well, maybe we’re looking at this the wrong way…maybe we don’t see so much of Raven’s leadership skills because she just doesn’t have reason to show them—it’s not her “job” in the team.
Or, maybe, she doesn’t want a command role, and so doesn’t flex that particlar “muscle.” In a pinch, in an emergency, she might take command, but that’s not the role she’d rather take. Spock or Data could take command of a ship—and they have, on occasion—but they excel in being a Science Officer or an Ops Officer.
In any case…if she was to lead a team (the Titans, or something else) I’d say that she’d need a good “XO” of her own to work with.
Dopers are the best. Next to Raven, of course. 
No doubt. Engaging in straight faced debates here about the Teen Titans has probably saved my relationship with my girlfirend who, despite assurances to the contrary, must be sick of hearing about it by now. 
The season finale will have a new team opening up in a new city, y’know: “Titans East” with “Aqualad, Bumblebee, Speedy, and a pair of high speed twins known as Mas y Menos” as the new team. I wonder if they’ll do a show on Speedy’s drug addiction…
“More and Less”? What are their powers?
Speedsters, apparently. The only thing I could find about them is some speculation that they may be sorta based on the Tornado Twins, Flash II/Barry Allen’s kids.
Well, I suppose since Wally is THE Flash now, there needs to be some kind of Flash-like teen hero in the Titans.
Two other factors as to why Robin is a better leader than Raven:
The first ties back into the idea that Raven is a loner whom the other Titans fear more than respect. In other leadership situations, this can be made to work. If we were talking about a naval ship during the Napoleonic era, then a remote autocratic leader is just what you’re looking for. If we’re talking about a marine drill sergeant, then a leader who can scare the crap out of the people he’s in charge of is what you want. Even in an office enviroment, someone who isn’t afraid to crack the whip and doesn’t socialize is desireable.
But this is a team of superheros. That’s a whole other kettle of fish. This isn’t the military, where you don’t have a choice about taking order, and this isn’t a regular employment situation, where you have to put up with a boss you don’t like if you want to get a paycheck. The only thing keeping the Titans from all going their own ways is loyalty to the group. And if the team leader is not liked and respected, there’s absolutely nothing to keep any team member from going their own way, or to keep the team from simply ignoring the self-designated “leader.” Remember, Robin is only the leader of the Titans because the rest of the team look to him for leadership. He has no formal claim to the position: he’s not been appointed by a higher power, nor (so far as I know) was he the founder of the organization, or owner of the headquarters and all the associated equipment they use to fight crime. He’s not a leader in the sense that the Titans have any sort of clear chain of command, he’s more of a “first among equals” sort of leader. And he has that position because all of the other Titans, Raven included, trust and respect his judgement and character. If he ever loses that trust and respect, or if his position in the group is ever supplanted by someone who doesn’t command that trust and respect themselves, then the Titans are finished as a superhero team.
The other factor is that there is really only one requirement for leading a team of superheros: you have to be able to beat up everyone else on the team. Robin is the only Titan who can make that claim. Therefore, he’s the leader.