This is going to be based off the current list. Bold = Change
Abomasnow - I feel Abomasnow should go down to the UU list. Snow Warning might be overpowering for the UU environment, but I see Weather Teams being used more often in UU. It has one of the worst 4x weaknesses to hit this generation, which is Fire. As we've seen, Fire-type usage has risen ten fold. Its normal defense isn't exactly as high as I would like for it to live through a Flare Blitz, Blaze Kick, Fire Punch. Even with its exceptional HP (Maxing to 384). We can't forget its weaknesses to Fighting, Steel, Bug, or Poison either. It does have sizable ATK & Spc. ATK., but I'd go out on a limb and mention Arcanine, whose BP Average is much higher in both categories.
Alakazam
Ambipom
Arcanine (Earthquake would so make Arcanine OU)
Articuno
Blaziken
Charizard
Claydol
Cloyster - I think Cloyster is basically a Forretress with higher defense, but lower everything else. Not to mention it being a different type. It's something I wouldn't find in a BL or OU environment. So, I'm going to say that Cloyster belongs in the UU tier.
Drapion
Dugtrio
Empoleon
Entei
Espeon
Exeggutor
Floatzel
Flygon
Forretress - Forretress is still common, I see it all the time. It's job is still to support, which it does quite well. Not mention that it stalls, but holds the deadly Fire weakness now. Not only can it learn both Spikes and Rapid Spin, but it can now support Stealth Rock via TM. Plus, it has Explosion on the side that we all know and love. I recommend moving Forretress to OU.
Gardevoir
Hariyama
Honchkrow
Jynx
Kingdra - I'm a bit mixed with Kingdra, but I'm a little slanted to say that Kingdra should go to OU. I do see it (ignore self) on Shoddy, and it has good overall stats. Not to mention that it's only weak to Dragon (Though Dragon's a much more common move type) so it has steady support on its own. It now has physical support with Waterfall to actually make it a viable Dragon Dancer. Add the godly Sniper and Scope Lens to it, and fuck. Need I say more? Oh, of course, we can't forget its super special attacks in the fray.
Leafeon - I love its other stats a lot, but it's just not versatile enough for OU or BL. If its move set was more broad, then I could see a lot more going for it. However, it's just not worth it. UU for Leafeon.
Lickilicky
Ludicolo
Machamp
Magmortar
Marowak
Medicham
Mesprit
Milotic - Milotic is still here and there. It's still the annoying tank as it ever was, and it has a better chance to put something to sleep. OU.
Miltank
Mismagius
Moltres
Ninjask
Porygon2
Ramparados
Regice
Regigigas
Regirock
Registeel
Roserade - Honestly, I've only seen this thing one time, and that was with Space. It doesn't do much at all as far as I can tell. Roserade should be sent to UU.
Sceptile
Scizor
Scyther
Slaking
Shaymin - It may have a crappy moveset, but that doesn't allow it to enter the BL with Mew-type stats. Set it in OU, and it'll avoid some controversy.
Shedinja - All Shedinja got was a Focus Sash, and that was it. Not much changed with it. Unless it can be used as a better Baton Passer, then I'm going to say that it should live with the UU folk.
Smeargle - OU. Smeargle is the most broken Baton Pass user ever, even if it's not on a Baton Pass-Based team. I've actually seen Smeargle on unfocused BP Teams.
Snorlax
Spiritomb
Staraptor
Steelix
Suicune
Tauros
Torterra
Umbreon
Uxie
Venusaur
Yanmega
Zangoose - I've never seen Zangoose as much of a threat in ADV, and I don't see it as much of a threat now. It does have super attack and speed, but it can't last. It's more of a revenge Pokémon than anything else. I recommend it be pushed down into the UU tier.
Zapdos
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Certain Baton Passers should consider being put into the OU bracket alongside Smeargle. I can't decide on which ones however.