Bumping....
First, Hoopa-U was banned so lets get rid of that. Here are some other noms:
Landorus-T S -> A+: So this was mentioned before and I would like to reiterate and stress it once more. Landorus-T to me faces the same problems in STABmons as it does in OU, in which it tries to compress to many roles in one slot. Although it can do this to an extent, you simply cannot cover all the threats you want to and threaten the majority of walls at the same time. Bulky SR sets are usually stopped by fat mons and offensive sets cannot check power physical attackers such as Mega Charizard-X and Terrakion all that efficiently. Its a great mon when it gets to do what it was intended for, but the lack of consistency does not place it as a S-Rank mon imo.
Mega Diancie A -> A+: This mon is super scary and is definitely above all the other A-Rank mons right now. Physically orientated mixed sets are extremely efficient (ie: Diamond Storm, Play Rough, Earth Power/HP Fire, Protect) and lets Mega Diancie check many top threats in Mega Zard-Y, Tornadus-T, Kyureum-B, and Latios. The lack of speed prematurely and its weakness to Bullet Punch does hinder it slightly, but overall Mega Diancie is a great offensive threat that is especially good since its not weak to FakeSpeed.
Clefable A -> A-: So I have been trying to use Clefable and it hasn't really been offering that much. CM Unaware sets don't really wall much stuff since everything has powerful moves now compared to OU, and its lack of solid bulk really hinders it from effectively walling setup sweepers. The transition to a more offensive metagame just does not really help Clef in the longrun, as it cannot keep up with certain threats (for Ex: Lando can now 2HKO defensive Clef with Precicpice Blades and Dragon Ascent, Thundurus can wall out Clef with Oblivion Wing, Serperior can put Clef to sleep, etc..). Its a great mon, but can sometimes lack on certain areas at time.
Starmie B+ to A-: I love Starmie as an offensive spinner as it can beat out most hazard setters and can remain an offensive threat with its high base speed and decent Special attack. Water/Psychic is great typing in conjunction with its moderate bulk as well, which gives it many opportunities to get a spin off. The use of Scrappy spinners and Pursuit does overshadow it a bit, but it still can outlast these shortcomings most of the time (at least with my testing), and can definitely be brought up to the A rankings because of this.
I will shut up now and let others discuss :)