Gen VII -
Alolan Sandlash is cool and Kartana is one of the few good Ultra Beasts, but overall a very weak lineup.
Gen IV -
Lucario, Magnezone, and a bunch of bad.
Gen I -
Two solid Pokemon, but a very limited roster and Magnezone is better. Only putting it above IV because IV has so many bad Pokemon.
Gen VI -
Aegislash is awesome and Mega Lucario is pretty cool, but I don't care for Klefki or the other Megas.
Gen II -
A small group here but all of them are a least decent, with Scizor and Skarmory being better than decent.
Gen III -
Also a small group, but Aggron and Megaross rule, and even Jirachi is pretty good.
Gen IX -
Tinkaton, Orthworm, and Kingambit are great, and I like Gholdengo too. A really good lineup overall but the gens above it are stacked.
Gen VIII -
Corviknight and Perrserker are fantastic and the elephants are really good. The legendaries are pretty solid too. The only dud is Stunfisk
Gen V -
Bisharp is my favorite Steel type, so this gen gets an automatic boost from that, but Excadrill and Escavalier are top tier Steel types too. Genesect has a sweet design and I would like it a lot if it wasn't a Mythical. The seeds and gears are pretty funny and decent in their own right. Cobalion I don't really have any strong feelings about.
Also, while we're on the subject I need to make a complaint about Escavalier. Let's look at it's Pokedex entry for Pokemon Black:
They fly around at high speed, striking with their pointed spears. Even when in trouble, they face opponents bravely.
Speed: 20
wtf