S+:
Clefable (Specially Defensive Unaware set is what truely shines in this meta as it counters both Latios and Manaphy. Other sets does their job well too.
Extremely threatening with the setup sets either by Calm Mind or Cosmic Power, be aware that Spdef Scizor fails to beat it)
S:
Latios (Very self explanatory, Specs / LO can absolutely dismantle unprepared teams)
Scizor (Mostly seen with investment into special defense, bulky enough to check a lot of threats and gain momentum through U-turn, and Bulky SD set sweeps very well in mid-late game)
A+:
Breloom (A lot of teams struggle against Spore, and LO mach punch is not easy at all to take)
Garchomp (Even more threatening to play against defensively than Latios, Band, SD LO and Scarf all have their unique functionality)
Magnezone (Essential part of the DragMag strategy, very strong due to Latios and Garchomp)
Starmie (Very quick Rapid Spinner, do not underestimate its attack power! Natural Cure and Analytic are distinct ways to play it but they are both useful)
Weavile (Basically the fastest unboosted pokemon in the meta apart from Aerodactyl, SD and Band can both punch holes, however weakness to Mach Punch and Bullet Punch limits it by quite a bit)
A:
Alakazam (Hits like a truck at +2 and Sash gives it big advantage in trading)
Blissey (The bulb, Calm Mind sets recently performing better than expectations)
Gliscor (Rocks setter / Defogger that is not afraid of chipping, can also grab momentum with U-turn)
Manaphy (Destroys balance with Tail Glow boost, but suffers against Stall and is not very impressive against offense. Chesto Rest set can be used to trade better with offense)
Rotom-Wash (Great Pivot that can check Scizor, and also has Trick to dismantle stall)
A-:
Gengar (Sweeps after Nasty Plot and cannot be stopped by Blissey, but does suffer against faster pokemons and priorities. Also hits quite weak without the boost)
Heatran (Still strong but gets limited by the common pokemons like Gliscor and Garchomp, quite a few people takes Flame Body to attempt to burn Scizor. Very effective counter to Clefable when equipped with Taunt)
Infernape (Another good stealth rocks lead, but also has a lot of uses other than leading such as breaking / revenge killing, has no real switchin before set is revealed but suffers a lot from 4MSS)
Latias (Not as commonly used due to Latios being better a lot of the times, but better bulk / Healing Wish has its values)
Mamoswine (Great coverage with Ice / Ground STABs and can also set up rocks, be careful of its freeze-dry!)
Rotom-Mow (Scarfer with Trick and kills Manaphy, very pressuring with the ability to Nasty Plot after using trick)
B+:
Azelf (Solid lead for HO)
Azumarill (Choice Band / Belly Drum are both hard to deal with altho Band is much easier to use, Fairy type helps against the dragons too)
Roserade (Very versatile with Spikes and Toxic Spikes, Sleep Powder and Grass / Poison STABs, deals with Breloom and can also be scarfed to deal with Manaphy)
Skarmory (Excellent physical wall that can set up Spikes, also seen as lead but less relevant)
Slowbro (No Teleport sucks, but still tanky enough to take hits. Future Sight is not as good)
Tangrowth (More defensive answer to Breloom that also keeps physical water attackers in check)
Tyranitar (Rocks setter, Band / Special / Mixed / Defensive are all viable and can fit into different teams nicely, often bait kills Gliscor and Scizor)
B:
Bronzong (Rocks setter that counters Latios, surprisingly effective in offensive teams)
Cloyster (Sweeper but losing King's Rock is very painful. Also requires appropriate hazard control from teammates)
Crawdaunt (Hits really hard but is hindered by its slow speed)
Feraligatr (A threatening sweeper under specific circumstances)
Mantine (True Manaphy counter, also beats a lot of other setup pokemons such as Latios and Clefable)
Mew (Does a lot of different stuff and excels at none, but will be much more used after the more powerful breakers such as Manaphy gets banned)
Nidoking (Another Rocks setter that pressures defoggers a lot)
Quagsire (Enjoys the meta lacking Toxic and has Toxic himself)
B-:
Aerodactyl (Fast Rocks lead that almost guarentees rocks on opposing team at the cost of its own life, can't deal with some Rapid Spinners though. Has a niche to beat opposing Azelf leads, giving a huge advantage in HO vs HO)
Donphan (Anti-lead thats durable and hits decently hard)
Dragonite (Can sweep but demands a lot of support from teammates in order to function, recently seen a few times as Special / Mixed attacker as well)
Gyarados (Can force sweep in late game but generally inferior to other water attackers due to lack of immediate power and ability to wallbreak. Hurricane can really catch Tangrowth offguard tho)
Lucario (Can boost with both SD and NP, making it very unpredictable. Speed is subpar though)
Shuckle (Webs setter that lost encore and gives free setup for opponent, but still has Toxic)
Smeargle (Webs setter that doesn't give too much free setup for opponent but dies to anything you can imagine)
Togekiss (Paraflinch and tanky enough to check the dragons)
C+:
Blastoise (Shell Smash abuser but gets stopped by Manaphy counters)
Cresselia (Trick Room user but more commonly seen as a fast Calm Mind user right now)
Froslass (Spikes lead that also blocks Rapid Spin)
Hippowdon (Solid physical wall but lacking Toxic makes it extra hard for it to retaliate)
Raikou (Sets up with Calm Mind but lacks the coverage / power / speed / durability to abuse it against most teams, still works late game.)
Staraptor (Very powerful normal-type attacker but lacks longevity)
Torkoal (Useable in both sun teams and Trick Room teams)
Venomoth (Niche pokemon that takes advantage of teams lacking counters to it with Sleep Powder)
C:
Ditto (Anti-sweep and also annoys stall)
Entei (Band Entei hits very hard and can catch people off guard)
Honchkrow (Sucker Punch and Moxie forms an unique way of sweeping when properly played)
Jirachi (Does not have Iron Head and utilizes Doom Desire instead)
Machamp (Fearsome wallbreaker but is very slow)
Shedinja (Latios and Manaphy counter but is afraid of any form of chip)
Suicune (
Just use manaphy instead Bulky water type that can set up with Calm Mind)
Uxie (Trick Room setter with U-turn and rocks)
C-:
Espeon (Has Magic Bounce to take advantage of passive pokemons, but lacks Power / Coverage to be effectively offensively)
Linoone (Belly Drum Espeed can sweep late game but is hard to pull off even with screens on, and lack of coverage hurts its viability too)
Metagross (Checks Latios and hits quite hard but lacks recovery / power / coverage to be effective. Scarf can surprise people at times)
Porygon-Z (Hits hard but struggles in the current meta that lacks slower balanced teams)
Salamence (Decent sweeper but has little use compared to other dragons, but can be used defensively due to Intimidate)
Victreebel (Sun team sweeper that can be unpredictable at times due to potential to use both physical and special moves)
Xatu (Screens setter that has Magic Bounce)
Yanmega (Takes advantage of HO that lacks Flying / Bug resists, functions well when opposing Scizor is down)
Feel free to suggest pokemons that I might've missed / misplaced in this list :)
Edit 1: Updated at 12/6 with a lot more gameplays and obs