Okay, I suggest we all post what we think should be the 5 S-ranked Pokes (I am limiting it to 5 because that's already a lot, imo). The others that will be moved to A can be posted separately. I will begin with Victini:
Victini is without a doubt S-ranked material now that the meta has shifted towards the influx of Nidoqueen, Rhyperior, and more Physically defensive 'Mons tailored to counter common physical threats, namely Mienshao, Heracross, and most Victini.
Victini is one of 2 pokes in the UU tier that can effectively run a mixed attacking set, the other being Virizion. What makes Victini so deadly is the combination of bulk, offensive typing, and move-pool. Unlike most heavy hitters, such as Heracross, Mienshao, and Azelf, Victini boast 100/100/100 bulk. This allows it to take most neutral hits moderately well. For example, it can come in defensive Roserade's sludge bomb, Scarfed Reckless HJK from Mienshao (My parallelism is off, but I'm just writing this down as an informative. Please excuse me; I can type with better English if anyone wants), and Suicine's Scald. With this bulk, it can retaliate back with a powerful V-create, Zen Headbutt, or Bolt Strike. However, this being said, it also has the needed speed to outspeed certain threats, such as Honkcrow, Specs Chandelure, and the likes. This base 100 speed also allows it to speed tie Shaymin, Mew, Zapdos, Flygon, and many other Pokes in the UU tier. This is different than Banded Snorlax, who has the bulk to take a hit; however, it will almost always take a hit before hitting back. Victini can take hits from slower Mon's, however, a lot of the times it simply does not need to. On the contrary, a Pokemon like Azelf lacks the move-pool to be an immediate wallbreaker, so it will have to take a hit--and most neutral moves are a 2HK on said Azelf.
Secondly, Victini's offensive typing is pretty awesome. Fire STAB is something that almost every team needs. For instance, most people opt to run Heat Wave on Zapdos juxtaposed to Extrasensory--why? Because Fire-type moves are good at frying Froslass, Roserade, and Bronzong. With STAB, it can OHK most Bronzong with Fire Blast (Not even Blue Flare), something Azelf cannot do. Psychic also compliments Fire, hitting most Water Types for neutral damage. It is pretty much only resisted by other Victini and the likes.
In addition to it's bulk and typing, Victini has an amazing move-pool. The Physical set has destructive moves in V-create and Bolt Strike, whereas you have other options with coverage, namely Zen Headbutt, Fusion Bolt, U-Turn and Brick Break. This is rather expansive movepool for a physical attacker. On the special side, we have Blue Flare, Fire Blast, Grass Knot, Psyshock AND Psychic, Shadow ball, Focus Blast, Glaciate, and Hidden Power. The Physical sets absolutely destroy Empoleon, Umbreon, and Hitmontop, some very sturdy walls in UU. The Special set kills Slowbro, Swampert, and Rhyperior. Victini can run a deadly revenging scarf set using it's physical movepool, or it can be a wall breaker with a choice band. If you want to lure, use an Expert Belt set with the physical AND special moves of your choice. If you want to nuke the common counters, go use a Life Orb Special set. Watch as you OHK standard Rhyperior, Swampert, and 2hk others!
Victini, in my opinion, is like Jirachi in OU. It has the bulk to do anything, and it does everything well; however, it is not broken. It has many flaws. It's main move, V-create, leaves it easily pursuit trapped, lowers its defenses, and makes it very revenge prone. It is weak to ALL hazards and cannot break through certain checks once the full set is revealed. For example, a Rhyperior WILL wall the physical set, and Snorlax WILL wall the mixed set.
I left out the ability because it speaks for itself. So yeah, vote for it to stay...
ALSO IT IS S-ranked :B