Decks to look out for:
1. Gallade (SW) variants - there has been a lot of hype surrounding this card, and for good reasons. I'm expecting it to win many Cities.
2. Blissey (MT) variants - this will be beaten by Gallade, but it will still be big due to it's performance at BRs.
3. Empoleon (DP) variants - This has always been a solid choice, so why should it be any different at Cities? Well, apart from Ampharos, nothing.
4. Mario - yet another solid choice of a deck, I'm expecting it to struggle more than it has in the past due to the new Gardevoir.
5. T2Banette - I have heard a lot of people are testing this deck, and this is another hyped card. It should see a lot of play and win a few Cities as well.
There are plenty of others that will see play, but I don't think they won't do as well as those 5. This includes the like of Ampharos (SW) variants, Kingdra Swarm, MegaGatr, Hurricane, Blastoise (SW) variants, and Hand Control decks.