My prediction:
5. M Sceptile Variants -There's a lot of variants that could be used (M Sceptile/Vileplume, M Sceptile/Lugia EX, M Spectile/Ariados) which is why I put this at number 5.
4. Primal Groudon - Even with the grass decks to come, Primal Ground EX's ancient trait, bulk, and power will keep it alive. It loses near to nothing from the rotation, and Weakness Police can help with bad match ups.
3. Riachu/Bats - It's just a REALLY solid deck. Has few bad match ups.
2. Vespiqueen/Eeveelutions - From what we know of Plasma Flareon, it's simple to see why Vespiqueen will be a good deck. It can hit for good numbers, can retreat for free, only gives one prize, sets up fast, and has little counters. The Eeveelutions also can give it the edge of hitting for even more weakness, while also having a great type for decks like the Primals and Seismitoad. Also Level Ball is crazy good in this deck.
1. Metal Rayquaza - It's a well rounded fast deck that placed very well at US Nationals. It also has little to weakness that can't be solved.
There's a lot of good decks that could see use (Machamp EX, Gallade EX, Giratina EX, Shiftry, Night March, M T Tar EX) but they'll be out-classed by some of, if not all of these decks. That's not to say you shouldn't build them and give them a go, if you're a good enough player/deck builder you could make them work and profit for you.
Prove me wrong.
Pro Tip: You can't.