I'd like to suggest Kyurem-Black for A-.
I've found that Cube performs amazingly in this meta. Teravolt is really nice for breaking things like Rotom-W, Dragonite, Mega Venusaur, and Rhyperior. It has ungodly 170/120 offenses and just good enough a movepool to make use of them. Its 125/100/90 defenses are great, and its base 95 speed, while by no means ideal, gives it a decent speed tier. Regardless of set, it can revenge BD Azumarill, Diggersby, Crawdaunt, TG Manaphy (barring Wacan sets), and (Mega-)Gyarados lacking Stone Edge.
The scarf set can revenge all kinds of shit, like Adamant Charizard-X and Dragonite (even when multiscale is intact) after a DD, Mega Pinsir, SD Garchomp, SD Terrakion, and Lucario that lack Bullet Punch. Scarf also lets it beat Keldeo, Lati@s, and Scarf Landorus-T. Besides R-Killing all kinds of threats, late game it can just come in and clean up by spamming Outrage.
A set that I think is really underrated is an Assault Vest set. I've been using this a lot lately and it has been working wonders. This allows it to easily take on shit like Greninja, Mega Manectric, Raikou, LO Gengar, Landorus-I , Thundurus (can't switch in on Focus Blast from these three, other attacks no problem and can take a focus blast if it gets in safe), and Omastar (can't switch in on Shell Smash sets, but can take a hit and KO back, even after Rocks: +2 252+ SpA Life Orb Omastar Hydro Pump vs. 48 HP / 0 SpD Assault Vest Kyurem-B in Rain: 256-302 (63.5 - 74.9%) -- guaranteed 2HKO after Stealth Rock), and Mega Charizard Y (Can only switch in on Solar Beam)
With the current Metagame overflowing with Greninja, Gengar, Electrics, and Rain, being able to check (Counter in the case of Greninja and the Electrics bar Thundy) the above threats all with one pokemon is amazing. Also, if a set of Fusion Bolt/Ice Beam/Earth Power/Iron Head is used (which IMO is optimal) Mega-Gardevoir, Clefable, Mamoswine, Weavile (barring Low Kick), and Sylveon can be beaten.
Other sets such as Sub + 3 Attacks and LO Roost + 3 Attacks also seem pretty damn good but I haven't used them enough to really comment.
Now, Cube does have its fair share of problems, such as a generally bad defensive typing, an SR weakness, and a somewhat middling speed tier, but all the support it really needs to do its job well is Spin/Defog support, which most teams can provide with little cost.
A Rank: Reserved for Pokemon that are fantastic in the OU metagame, and can sweep, support, or wall significant portions of the metagame. These Pokemon require less support than most others to be used effectively and have few flaws that can easily be compensated for when compared to their positive traits.
To me, that describes Cube very well. It beats mons that are really common in the current meta, needs very little support to do so outside of SR removal, and its prowess at what it does easily compensates for its flaws.
I think Cube is easily on par with some other A- mons, like Manaphy and Mega Aerodactyl, and I certainly think it is better than some other B+ mons like Alomomola and Celebi in the current Metagame.