Aerodactyl doesn't have much that Tough Claws boosts. Stone Edge, Rock Slide, Earthquake, etc. are not boosted, so it's stuck with stuff like Aerial Ace, Iron Head, Crunch, and Double-Edge for Tough Claws. I really can't see it doing that much damage even with Tough Claws.Abomasnow may end up UU, especially since weather isn't perma anyone, and I know its mega has scary attack stats but it's slow as dirt and remember that it can't hold an item to boost those stats. 132/132 is still weaker than 100/100 with life orb, which multiple things have in UU. It's still weak to all hazards (except sticky web I guess), and still has one of the absolute worst defensive typings possible.
Manectric is probably UU too, it's pretty outclassed by Raikou unless you really like overheat, but then again overheat makes it setup bait after a kill. Raikou has better bulk, doesn't take a mega spot, can run way more sets, is able to hold different items, etc. I just don't see any reason to run manectric unless you really want your electric type to outspeed base 116+ pokemon.
Aero is probably the closest either way, although I wouldn't be surprised if they BL'd even if the usage stats didn't make it OU. It's weak to priority, but that's what teammates are for. It's weak to rocks, but learns roost. Tough claws helps give it great coverage, but the coverage moves (fangs and such) themselves aren't that strong. Hard to say, hard to say....
Manectric is a good speedy pivot with Intimidate and its Speed, as well as Lightningrod the first time you come in. Volt Switch lets you switch between Manectric and something like Gyarados to abuse Intimidates. However, its stats are not too good outside of Speed, as without an LO its Special Attack is quite manageable.
Mega Abomasnow is an interesting option for Trick Room teams, for sure. It's also very usable on normal teams, but now that Hail teams are completely dead, Mega Abomasnow doesn't really bring much to the table, especially in a metagame dominated by Fire-types. I daresay it's even bad enough for RU this gen, because 132/132, while good for RU, is mediocre compared to CB Entei, LO Hitmonlee, CB Medicham, LO Clefable (may move up), CB Durant, LO Vivillon, etc., and some of the aforementioned can set up, while Mega Abomasnow can't. Also those defensive stats are some of the biggest wastes in the history of wastes, coming with the second worst defensive typing in existence.
As for the other Megas, only Charizard, Mawile, Lucario, Pinsir, Tyranitar, Scizor, Garchomp, Gyarados, or maybe Absol would have chances at OU this gen. Charizard hits really hard with Fire Blast, and you'd better have a Fire resist with you. Mawile hits super hard. Lucario can sweep with SD or NP. Pinsir is a really good SD sweeper. Tyranitar, Scizor, Garchomp, and Gyarados are OU without their Megas, and the former three won't even use them most of the time. Absol...it has Magic Bounce I guess? And 150/115/115 offenses are nice, but it's relying on Sucker Punch for its STAB...