I might be getting too far ahead of myself, here, especially since I don't even know if I'll be able to buy the game, but I think it's probably Alola ninetales now.
I say "now" because for more than ten years, gardevoir has been my pokemon; the one I wanted with me everywhere; she hasn't been completely dethroned yet (mostly because I don't know ninetales' more technical details), but the fact that after having her for so long, and even after her becoming a fairy type, ninetales made me consider her not being my signature pokemon anymore, when others like mismagius, meloetta, glaceon and articuno couldn't, is significant enough.
Together they would be best, but there can only be one, sadly.
Besides, it always felt weird not having my favorite pokemon be of my favorite type, anyway.