Red/Blue: Ooof... this is pretty tough. Actually, it's an easy win. Red.

Gold/Silver/Crystal: Crystal. Easy win. Why, you may ask? Celebi.

Ruby/Sapphire/Emerald: Emerald. You can have both Legendaries and several exclusive N-dex* Pokémon.

FireRed/LeafGreen: FireRed. It just has the bigger selection, and the bigger the better in some cases.

Diamond/Pearl/Platinum: Pearl. Salamence is the only reason why.

HGSS: HeartGold. If Donphan was a little bit faster, SoulSilver would've won.

Black/White: Honestly, White has Thundurus, an Electric/Flying. Better typing than Tornadus.

B2/W2: Black 2. Easy win tbh.

X/Y: I have to give it to Y. Heracross, Aromatisse, the OP version of Charizard.

ORAS: Alpha Sapphire. Water is better than Ground, obviously.

Sun/Moon: Sun, honestly. Turtonator is much better than you'd expect.

Let's Go: Alolan versions are better in Let's Go Pikachu than Let's Go Eevee.

SwSh: Sword. Zacian is the better Legendary than Zamazenta by a landslide.

BDSP: Shining Pearl. See Diamond, Pearl & Platinum for more information.

Sc/Vi: Ooh... this is a tough one. I'll say Scarlet. Koraidon isn't the better Legendary, but the future Paradox Pokémon? Yikes.