My vote goes to Gen 6.
>Greninja
>Honedge line
>Furfrou
>Aromatisse line
>Clawitzer line
>Heliolisk line
>Tyrantrum line
>Carbink
>Trevenant line
>Xerneas and Yveltal
These are all some of the best shinies in the entire franchise.
They actually tried with this gens shinies, which can't be said for many others. But maybe you can prove me wrong.