Which generation has the strongest Pokédex lineup overall?

This is inexplicably hard but I think im going to go with Gen 5 on this one despite how crazy high you have to go to evolve some of the new additions. Independent of the starters, Lillipup is actually a pretty solid early game Normal type that many speed runners use due to its versatility and early game power. Elemental Monkeys give you an early game edge on your rival, particularly if you're able to evolve them via Stone for the power spike. Unfezant is probably the least popular regional bird and is probably underwhelming given Staraptor the region prior but they buffed its Attack by 10 points and has Super Luck to go with solid speed(loss of Return really hurt).

Then there's Sawsbuck, who with Ferrothorn, Leavanny and Amoongus are solid Grass options if you didn't take Snivy as your starter. Chandelure, Darmanitan and Volcarona are Fire type alternatives for Tepig users(latter comes insanely late though). Water options aren't that great and is probably why Oshawott is so popular(changes in the sequel with Azumarill and Vaporeon just to name a few) but that doesn't mean Jellicent or Swanna are bad if you didn't like the Elemental Monkeys. If you didn't like Unfezant, you got two more Bird options in Braviary and Mandibuzz.

Krookodile, Golurk and Excadrill are insanely good Ground types. Bisharp was awesome before Kingambit came along. Hydreigon is the regional Pseudo with Druddigon and Haxorus joining it as other Dragon alternatives. Ice types had Cryogonal and Vanilluxe.. I mean everything they added isn't that bad. Even the Fighting types aren't horrible and then there's the Joltix line, Emolga, Zebstrika, and Eelektross for Electric types and I didn't even mention Klink or the Legendaries.

This helps too.

This is a really tough choice… I have no answer.

That's… quite the argument you're putting up for Gen 5… honestly reading it I agree now.

I feel there is some growth happening in the games. Or I just really liked Violet. I like the variety of types.

Generation 1 and 5 stand out because of their Pokedex being entirely encompassed with new Pokemon(or mostly new). Having an adventure that gives me a challenge in determining which pokemon is advantageous is equally important.

The one thing every generation has given. The one thing that rules them all. Is having new combinations of strong pokemon and pokemon along the way to learn and focus on. Which is why I like every generation. And look forward to many more years of Pokemon.