I could write various reasons of why, VGC is better than Pokebank OU (In this season) but I wont... Fuk, I need to.
Pokebank OU is basically ORAS OU, with the addition of Z-Moves + a bunch of pokes. Still, same gameplay as it is for 2 years or so.
VGC17, instead, adds that variety onto the meta, refreshing and at the same time, nothing super weird. Some people dont like doubles at all, but come on, do you really prefer to always play the same, rather than changing things a bit?
Go and vote for VGC, and I´ll gib u cookies