If I might argue against Latios, I'd like to say why I don't think it should be in the top 10. Latios is extremely powerful and fast, and can be terrifying with Specs Draco Meteors and Psyshocks to get past Blissey and company. However, I do not consider it one of the best Dragons in OU (that's Garchomp and Banded Dragonite, easily. Even Latias is better than Latios, imo). There has never been a time when Latios was king. He has always played second fiddle to other OU Pokémon, never breaking past the point of "really good" and becoming "metagame defining." I think Latios has two great faults that keep it from being top 10 material: its main STAB forces it to switch out (or at least cripples it), and it is easily Pursuit trapped.
On the first fault, Draco Meteor is, as I said before, absurdly strong coming off 130 Special Attack, but unlike Kyurem-B, Garchomp, or Dragonite, using its STAB move means that it is officially crippled, ESPECIALLY if it is Choice-locked. I honestly don't think Latios is that good of a Scarf Pokémon in part because of this. Obviously it has it's niche as the fastest Scarfer in the tier (which, of course, shouldn't be taken lightly considering the popularity of Scarf Keldeo), but it also can't clean up like a Scarf Pokémon should be able to. Late-game, you can send in your Keldeo and spam Hydro Pump or Surf and win the game with it. Rarely will Latios spam Psyshock or Surf to win, and it can never "spam" Draco Meteor to clean up, because it simply becomes too weak after a single use.
As for the second fault, it sort of ties in with the first one: every time I see Tyranitar or Scizor on my opponent's team and I'm using Latios, I basically say to myself: "Well, shit. Looks like I'm not going to be able to use Latios until that thing is dead." Tyranitar and Scizor absolutely cockblock Latios in every match without very good prediction, the right coverage move, and LO or Specs. And even IF Latios has Specs Surf, it most likely won't matter whether you use it or not. The opponent can simply find out what Latios is locked into my sacking the current Pokémon on the field, or a weakened one, and immediately send in Tyranitar to Pursuit. On top of that, this is only assuming BAND Tyranitar. Scarf doesn't care whether you have Specs Surf or not because it's going to KO you regardless. So the top two play styles (rain and sand) both have strong answers to Latios without even trying. I just don't think that is something that screams "top 10."
Furthermore, I think a major reason why Latios just isn't what I would pick for this slot has to do with the fact that Latios just hasn't affected the metagame outside of making Jirachi a bit more popular (though I assure you, it would still be very good even without Latios). Please—and this is not meant to be sarcastic or digging to anyone who believes Latios deserves this spot; I'm genuinely curious to find out—how has Latios influenced the metagame in a way that Latias hasn't? Latias is the best tank in the tier. I use Latias on teams because it checks sun and rain while hitting close enough to a hard as Latios that I don't really miss the extra power. There are so few times when I use Latios where I couldn't be using Latias in the same spot more efficiently. The only time I can think of when Latios is better is when using it as an offensive wallbreaker with the Specs set. Latias simply cannot match that power. Outside of that, though, I think Latias has much more utility.
Finally, I want to make sure everyone knows that I don't think Latios is bad by any means. I just think it is too easily stopped and not nearly as influential to BW OU as some of these other Pokémon are/were.
On the first fault, Draco Meteor is, as I said before, absurdly strong coming off 130 Special Attack, but unlike Kyurem-B, Garchomp, or Dragonite, using its STAB move means that it is officially crippled, ESPECIALLY if it is Choice-locked. I honestly don't think Latios is that good of a Scarf Pokémon in part because of this. Obviously it has it's niche as the fastest Scarfer in the tier (which, of course, shouldn't be taken lightly considering the popularity of Scarf Keldeo), but it also can't clean up like a Scarf Pokémon should be able to. Late-game, you can send in your Keldeo and spam Hydro Pump or Surf and win the game with it. Rarely will Latios spam Psyshock or Surf to win, and it can never "spam" Draco Meteor to clean up, because it simply becomes too weak after a single use.
As for the second fault, it sort of ties in with the first one: every time I see Tyranitar or Scizor on my opponent's team and I'm using Latios, I basically say to myself: "Well, shit. Looks like I'm not going to be able to use Latios until that thing is dead." Tyranitar and Scizor absolutely cockblock Latios in every match without very good prediction, the right coverage move, and LO or Specs. And even IF Latios has Specs Surf, it most likely won't matter whether you use it or not. The opponent can simply find out what Latios is locked into my sacking the current Pokémon on the field, or a weakened one, and immediately send in Tyranitar to Pursuit. On top of that, this is only assuming BAND Tyranitar. Scarf doesn't care whether you have Specs Surf or not because it's going to KO you regardless. So the top two play styles (rain and sand) both have strong answers to Latios without even trying. I just don't think that is something that screams "top 10."
Furthermore, I think a major reason why Latios just isn't what I would pick for this slot has to do with the fact that Latios just hasn't affected the metagame outside of making Jirachi a bit more popular (though I assure you, it would still be very good even without Latios). Please—and this is not meant to be sarcastic or digging to anyone who believes Latios deserves this spot; I'm genuinely curious to find out—how has Latios influenced the metagame in a way that Latias hasn't? Latias is the best tank in the tier. I use Latias on teams because it checks sun and rain while hitting close enough to a hard as Latios that I don't really miss the extra power. There are so few times when I use Latios where I couldn't be using Latias in the same spot more efficiently. The only time I can think of when Latios is better is when using it as an offensive wallbreaker with the Specs set. Latias simply cannot match that power. Outside of that, though, I think Latias has much more utility.
Finally, I want to make sure everyone knows that I don't think Latios is bad by any means. I just think it is too easily stopped and not nearly as influential to BW OU as some of these other Pokémon are/were.
