I'll give my thoughts regarding the current suspects and how they are performing in the metagame.
Deoxys-S: Interesting Pokemon. There are actually a few non-standard lead and non-lead sets that I've been trying that have been working phenomenally. Deoxys-S is one of the primary reasons that the other suspects aren't shining as much as they would otherwise be. Skymin has 127 base Speed and huge Special Attack and (worst of all) Serene Grace, but it's kept in check at least in part thanks to Deoxys-S. I will vote this thing Uber most likely. As the metagame changes, though, it might fade from grace. Right now, it makes for a frightening revenge killer and offensive cleaner in general. And it's one of the best leads I've ever seen used--the only thing stopping it from being overpowering as a lead is the fact that everyone is using a lead specifically geared to counter Deoxys-S at the moment, but that will obviously fade as time goes on, and Deoxys-S will likely remain an extremely effective lead.
Latios: To be honest, I haven't had much trouble facing Latios. But I will say this: before using Latios, I wasn't anywhere close to the leaderboard, and after using Latios, I simply shot up through it, so I can attest to its excellence. As for whether or not Latios belongs in Uber . . . frankly, I'm not sure. It's better than Latias, but the difference isn't much (people are just using the wrong Latias sets, in general; as Bologo said, some differentiation needs to occur here). Latios does keep the other suspects in check, however. I'll probably vote for Uber for this one regardless (one Lati is sufficient in OU, I should think; the prospect of both being on the same team, I am not so sure about, though using both in conjunction brought me great success on the ladder).
Shaymin-S: I'll almost assuredly vote for this for Uber. Right now, threats such as Scarfchomp, Latios, and Deoxys-S are holding this back from shining, but Shaymin-S is an absolutely devastating Pokemon. Its base stats, coupled with its movepool and Serene Grace, make it easily one of the most fearsome Pokemon in the tier at the moment. I guess I'll wait until one or two of the other suspects leave the tier before passing judgment, but right now, I can't really see this thriving in OU (unless all of the other suspects also stay in OU, in which case it wouldn't be so frightening). The Submin and Scarfmin sets are probably the best, though the LO set is also very threatening.
Manaphy: I've always favored this thing descending down into OU, and the current suspect situation has only strenghthened and affirmed this opinion. Right now, the other suspects are preventing Rain from being a viable strategy, but if Deoxys-S and Shaymin-S were to go, I would predict a rise in Manaphy usage. The Tail Glow set is decent. Not much to say here. I guess we'll see what happens down the line!
Latias: I'm in favor of keeping this thing in OU. It did perfectly well in the previous OU metagame and is doing fairly well in this metagame. It hasn't been "broken" in either environment. I've used it to great success, though I'll admit Latios is better. As someone suggested to me, Scizor doesn't expect HP Fire, for some reason.
Garchomp: Hm. This is very difficult. It's definitely underwhelming in the current environment, but that's because the other suspects thoroughly trounce some of its sets. With Latios, Deoxys-S, and Shaymin-S gone, it will become a lot better, but, honestly, I think that the OU metagame will be able to handle it even then (Scizor can revenge it, as people noted, and the presence of Latias would still deter it, so I don't think it would be as broken as it was before). If Latios or either of the other two suspects is kept in, I definitely want to see Garchomp given a shot. I've used all of its sets and I like most of them, though I have to admit that Yache Berry is not effective in the current metagame. I've even used Bulky Restalk Garchomp on a stall team, and that worked pretty well (Brightpowder + Sandstream support makes it incredibly annoying).
It's a fast-paced and fun metagame. Right now, the following Pokemon have been doing the most for me on my teams:
Latios
Deoxys-S
Bronzong
Tyranitar
Happy suspecting!