I might not be the most experienced player but I still think I can manage a nice grasp on the meta. So I do have some noms, hopefully they are well received. Obviously some of these have been said before, but I really enjoy and support some of them and disagree with others.
--> S-. Weav is truly a force to be reckoned with right now. Many games are decided on giving weav that Swords Dance and the power of Triple Axel with the priority of Ice Shard provides ample STAB both ways. Dark type is always nice and it checks what most consider to be the best offensive mon in the game right now. The only things holding it back from true S are the fact that fighting moves make it cry and accuracy issues in Axel (which may be just me)
--> A+. Just an all around amazing mon. It provides plenty of checks to many major threats and has an incredible utility movepool where it can serve various roles. Utility is king, and it especially helps that Fini can mostly shirk off major threats in the most popular core in OU right now: Pult/Shifu.
--> A+. I think Koko comes in as the best electric mon in the current OU meta. Not because of its ability to sweep like a traditional electric type, but because it is undoubtedly one of the absolute best pivots currently in the game. I absolutely love its ability to set up and I love the large movepool of useful niches it can fill and enjoy. The ability to fill many roles is just as important if not more than the ability to hit stuff until it dies so Koko deserves a raise off that merit.
--> A+. How has this mon not seen its rise yet? I don't often use it myself, but Torn is just an all around great mon. The longevity of it is terrifying and its movepool is quite powerful. The only thing holding it back from the level of respect that its earthy brother commands is the fact that its movepool is inaccurate and a little less versatile.
--> A. I think the big bug actually has a really nice spot in the meta right now. With a very nice movepool capable of threatening a lot of top mons and his typing he canbe a great ground/bird check and pairs super well with a mon like Glowking. I also want to point out I think the Rocky Helmet is the way to go for Buzz as it provides consistent chip at many of the mons Buzz can survive against as is like Urshifu and Kartana.
--> A. There's a lot of role compression in Scizor and I absolutely adore his current sand tomb set to deal with some potent threats such as heatran. While not usually the feature player on a team, it provides an excellent partner to many a mon.
--> A. I think everyone else will disagree, but I think the boom deserves the slight bump to sit among the A tier mons. Although it has a lot of threats, Grassy Glide go Brr is actually still a very strong priority move. It can OHKO Weavile (it survives an ice shard, even with a SD and glide has prio over Triple Axel if they do not switch) and Urshifu and has a sneaky OHKO on Pult with Knock Off if they are locked out of Draco Meteor or with prediction. I've also been a big supporter of dropping Wood Hammer and adding Close Combat, where it can then OHKO common switch-ins like Heatran. It still has some big weaknesses and checks, but I think the mons in the A tier all have similar weaknesses.
--> A-. I love Mew. If you read my comment, you would see that I highly value versatility, and Mew has that in abundance. You can do nearly everything utility-wise with this guy. Also Mew is hands down one of the better leads in OU.
/ --> B+(with Blacephalon possibly going A- soon even!) Ghost has always been strong, but the type finds itself in a very good place in the current meta. There really aren't that many checks, and the few there are can even be dealt with by these 2 ghost mons, albeit not as consistently.
--> B-. I actually really like Cloyster in the meta. By no means is he the best but the Shell Smash + King's Rock is a really annoying and, at the same time, really fun gimmick that can be surprisingly effective. Cloyster has too many downsides to be considered a top tier threat, but B- reflects mons you really shouldn't underestimate and need to at least consider more in teambuilding.
--> C+. Cratersmash sold me. See his post. Love it.
/ --> C+. Ok, I'm not crazy. I think Sun is a fairly decent archetype in the current meta. Venusaur has almost no switch-ins under the Sun and a banded V-Create under sun from these 2's common partner is about the scariest thing ever. Torkoal is clearly the best sun setter in the game, and where Torkoal goes Venusaur goes. I can say I could even see Sun move to B-, but I like to approach things with trepidation.
--> A. Will I get flack for this? I hope not. But 2 of the biggest threats in the OU force it to switch in Urshifu and Weavile and it really even struggles vs top utility like Tapu Fini. Is it still very solid? Yes., But it probably no longer deserves that cusp of the S rank.
--> A/A-. With ground being a nearly mandatory type in OU right now, the prominence of Lando, and the absolute lack of recovery for Zera it already had enough to stay out of the S tier. However, I think Zera is worse off then he was even recently. Koko is coming in as a rather superior Electric mon and, though I wouldn't say Zera is bad, his flaws are being exemplified because of it.
--> B+. I understand the viability of Blissey. I get that she checks some top mons, especially Pult. However, I really dislike the fact that physical wallbreakers, which are abundant in the current meta, cause such great pain to Bliss. If there were a couple less physical breakers popular right now Bliss would deserve to reside in the A/A- area like she does, but I don't think you can justify it with mons like Weavile, Urshifu, and even Buzzwole so abundant.
--> B+. For a mon that is a flying, electric type with Defog potential it isn't the best at any of those 3. There are better picks most of the time for a bird, better for an electric, and better for a defogger. Not saying Zapdos is bad by any means, and some teams can fit him if they try. But he finds difficulty justifying his use a bit.
--> B+/B. It really isn't that bisharp is bad. Actually, bisharp is quite good. It mostly is just the fact that there's very little reason to run it. Weavile is heads and shoulders above bisharp right now and it is going to take a really specific team to justify using this instead of the latter. Sometimes a mon doesn't need to be worse because of itself to drop, just because of a better option.
--> B-. When you can't get it done vs what I would consider the top 3 offensive threats in the game (Weavile, Pult, and Urshifu) you can't really justify being high on the Viability Ranking. Not to mention Kartana and Kyurem also checking it. Taunt has seen plenty of use as well. There really isn't much going for this guy unless everything goes his way.
// --> C+. I think it's been said before but Rain is relatively weak in the current meta. I love the archetype, but this is just not the time for it and the VR should reflect that. It is no better than Sun and I could even make the argument that Sun is maybe a bit stronger.
I hope these nominations seem reasonable. I'm not the best player but I love analysis. I'm also sure I missed a couple :)
--> B-/C+. Mandibuzz is truly in a bad place right now. With the rise of other birds that are nearly all around better equipped to deal with the current meta Buzz just kind of falls off.
The only one I don't really agree with is Mandibuzz. I think it's fine staying where it is right now, especially because it's one of the few mons that can check both Dragapult and Blacephelon specs sets as of right now. Two mons that are being top threats in the meta right now. It also does pretty well versus Lando, so it's not extremely outclassed by Corvi, still outclassed though. So it's fine in B- right now IMO.