Ahem.
I am going to break contention here and say that Starfire, despite having the ability to be near-invincible in battle except for some plot-convenient stupidity, is the weakest member of the team. Not because she's useless in combat, but because that's her entire schtick.
Beast Boy- Has the druid's wildshape ability, but on angel dust and steroids. He can change size between a eukaryote and a blue whale as a free action, and his animal forms are stronger than the actual animal. On the fan boards, people who say that he's the weakest member (when he, if he was a munchkin, would usually steal the show) apparently have never seen the sheer terror of a druid.
Robin- He is Batman's friggin' disciple, the original king of non-combat schticks. He's like Sherlock Holmes and James Bond together.
Raven- Can scry, look through other people's minds, and can move things around with magic. Can teleport the party out of danger.
Cyborg- He is a cyborg. This means that his super strength is better than Starfire's and can pretty much make any computer or electronic system his bitch. Since the series takes place in the near future, there are a lot of computers. Also can make a futuristic car from scratch.
Starfire- Has generally useless knowledge of unknown things (Raven and Robin's is better), can fly and scout (Raven's is better), and can make light.
Combat pair-ups:
Beast Boy- See above comment on wildshape, only his power is (or rather should) be more frightening.
Cyborg- Better super strength than Starfire's, unlike her. Also is a very good meat shield. Also has a laser cannon. Really, the only thing she has on him is that she can fly. And since he is a CYBORG, there's really no reason to believe why he shouldn't have rocket shoes installed right this instant, other than intruding on her schtick.
Robin- The fastest Titan where it counts. His devices ironically cause the hugest explosions; even though he should be a ranged attacker, he's untouchable in melee. If only he had super strength...
Raven- Has really strong and fast telekinesis. That'd be more than enough, but she can also cause materials to erode and can protect her teammates. Can also fly.
Starfire- Flies and shoots lasers. Has super strength, but it's functionally useless since she doesn't know martial arts (unlike Robin), cannot block or avoid attacks (unlike Raven, Robin, and Beast Boy), and can't take hits (unlike Cyborg).
So what have we learned from this exercise? It's that:
1) Simply having high numbers for your schtick (Starfire's melee was the second highest, her rate of fire was the highest, and she flew the fastest) isn't enough. You have to do something other than have the biggest numbers.
2) Characters should not be given the option of having no non-combat schtick.
3) While some overlap is fine, a character should REALLY have the opportunity to do needed things different than from what everyone is doing.
4) Just because your party is better with you than without doesn't mean that you're pulling your weight.
5) As Seanbaby put it, simply being able to fly isn't all that unique, even if you're the only one doing it.