I had all the Gen. 2 games, so Gold AND Silver
If I had to choose for B, Fire Red
C is a bit iffy. In the original games I chose Sapphire, but for the remakes, I had Omega Ruby
D I skipped Sinnoh
Unova is surprisingly the easiest. I chose Black for both the original game and its sequel.
Blue, but FireRed for whatever reason
Silver and SoulSilver
Ruby (but Emerald is better)
Diamond (but Platinum is better)
White and White 2
X
Sun and Ultra Sun
Probably Sword but it'll depend on exclusives