So I'm pretty sure, from experience and what I've seen in the forum, that:
Staraptor is broken:
Choice Scarf can destroy offense too easily, ohkoing most sweepers and 2hkoing many walls
Choice Band can destroy stall too easily, 2hkoing basically the whole tier (that I can think of)
Figuring out which set it is can often cost you a pokemon.
Baton Pass is broken:
Espeon and maybe Mew are the culprits. The fact that passing to Espeon auto-beats Roar and Taunt makes it a lot more difficult to stop BP. The only teams that couldn't be undone by Baton Pass once you figured out their counters were....ones with Murkrow. Mew is a suspect already, so it's role on baton pass (boost bulk, never die) is only more incriminating.
Chansey is centralizing, but not broken:
If you don't prepare for Chansey, you are probably dead, but I feel like there are enough ways to deal with it that it isn't necessarily broken. The fact that chansey is a "prepare for X or lose a majority of games" pokemon doesn't really make it broken. You could just as easily say the same thing about Gliscor (in OU) or Raikou (in UU), and neither are particularly broken. Chansey is the bane of glass cannon pokemon, but if your team has enough physical presence to take it down or enough vitality to shrug off Seismic Toss + Status, then you can play around it. I think it was Flareblitz (although I know he wants chansey banned) who pointed out that every one of his teams shits on chansey. I think it's extremely strong, but not broken.
Victini is less strong than Staraptor, but might still be broken?:
I'm not really sure about Victini - it seems like the speed and defense drops can put it in a situation where offense can sac something and do damage in return. Stall on the other hand, can do decently with prediction if it carries a bulky water and something to take electric attacks. Rhyperior shits on it, and is also amazing in general, so that's an easy fix. Still, it will wreck through unprepared teams, and will do sick damage to even prepared teams with prediction. Not only that, but it has plenty of sets it can run to deal with the Choice sets' counters, so I'm not really sure which way to go on this.
Unless my points decay a lot, I will have upper reqs, which is why I wanted to post my opinions here - I feel if I'm not required to post sentences that I should make sure to justify my opinions. If someone has strong opposition to something I said, I want to hear it before I vote.