Depending on how far you're willing to go into the future, considering all the cards & sets we currently have leaked/know of, I think that Rayquaza/Zeraora GX has a ton of potential due to its performance in Japan, and Naganadel GX/Stakataka GX is probably the best 2 hit KO deck we'll have for a while barring its potential set up issues without Lele.
On top of this, I think the double Solgaleo GX deck will become servicable once Alolan Ninetales GX (fairy type) releases. Pokemon searching (Beacon) + item searching (Guaranteed Rare Candy/Ultra Ball) all for 0 energy makes any stage 2 deck much more consistent during set up.
As far as immediately after rotation hits is concerned, I think Naganadel GX/Stakataka GX is a great choice, as well as Splatoon decks. I believe Buzzwole + Beast Ring will still see some play for a bit, but I haven't run the list myself to really know, and I expect to see Zoroark GX variants still as people are transitioning into the new meta trying to figure out what's good and expecting their main weakness, Buzzwole, to fizzle out a bit due to losing stuff like Strong Energy and Max Elixir.
EDIT: After another day of playtesting, I feel more and more comfortable saying that Naganadel GX/Stakataka GX, Solgaleo GX/Alolan Ninetales GX, and Rayquaza GX/Zeraora GX are my top 3 favorite decks. The win rates amongst them are fairly balanced, and they are all very consistent. Amongst them, I think Rayquaza GX has the edge. I've had games where I have 3 Rayquaza GX with 3 energy a piece, 2 Wishful Batons on two of them, and it's amazing.