I think of Cynthia as a mandatory 4 of, personally.
Outside of that, I think Sophocoles, Hala, and Copycat all have situational advantages while Sightseer -should- be the go to bonus supporter if you want reliable draw power. I don't really see anyone using Tate & Liza at this point, but I imagine they'll be used in some situations. I've just never been a fan of shuffle draw 5 and never will be.
Lillie is a good T1 choice in some decks, but I've started steering away from her in testing since I'm 9 times out of 10 in favor of searching than drawing (i.e. Fan Club or Steven's Decision). Depending on your deck, the odds of simply getting to a point where drawing up to 8 is actually viable doesn't happen that often. I'm on average sitting at 4 to 5 cards at the end of a T1, and if I'm going to draw 3 or 4 random cards off of that, just play Steven to search for 3, especially on T1. I also think that Steven's Decision has better value outside of turn 1. Steven's Decision is good anytime you don't think that attacking for turn is the best idea, which happens during the early game set up phases and occasionally during midgame lulls.
Quite frankly, I think the best immediate post rotation deck will be Gardevoir GX/Sylveon GX/Zoroark GX for several reasons.
1. The more good dragons get printed, the more easy wins Fairy type gets. Zoroark GX also destroys Dawn Wings Necrozma GX, which means this deck basically has an auto win against UNGX/Malamar.
2. Sylveon GX's Magical Ribbon is significantly stronger in a format with no N. You basically get to Steven's Decision on top of playing Cynthia every turn during the set up phase.
3. With the loss of things like Special Charge and Super Rod, Twilight GX and Diantha become the best discard recovery abilities in the game, exclusive to Fairy decks.
4. Sylveon GX is made further useful by the fact that searching 3 cards out of your deck and playing them down means that each Cynthia you play becomes more and more likely to hit crucial cards in the late game when you don't want to be using Magical Ribbon anymore. Deck thinning & shuffle draw go VERY well together.
5. Zoroark GX is guaranteed to show up between Pokemon Fan Club & Magical Ribbon. Less draw power in supporter cards means that Zoroark GX shines more, at least on the Trade ability. Again, the discard from Zoroark GX isn't even problematic in the presence of Twilight GX and Diantha.
6. Sylveon GX and Zoroark GX make this deck "Judge-proof." You will always have the ability to access more cards than your opponent through Magical Ribbon or Trade if they aren't playing either Sylveon GX or Zoroark GX themselves after playing Judge. Strictly by virtue of hand advantage, Sylveon GX & Zoroark GX makes Judge a terrible card to play if your opponent has either.
7. Gardevoir GX has a very obnoxious HP value that most Basic GXs will struggle to hit consistently, especially with no more Max Elixir and no more FFB to make them just as bulky as Stage 2s. On top of that, Infinite Force is still one of the best attacks in the game, period.
8. Secret Spring is indefinitely more useful than Malamar as you can attach energy anywhere, not only to the bench.
I've done a handful of playtesting, and the list of Gardy/Sylveon/Zoroark I settled on is currently the king of consistency for me. Nothing gets set up nearly as well, but Alolan Ninetales GX/Zoroark GX is a decent second place due to Beacon and free retreat from Tapu Koko Promo in a rotation with no Float Stone. Mallow/Zoroark GX combo is fantastic in the deck, and the return of Fisherman provides you with the option to turbo through your energy without fear.
I will also mention that Copycat is a fantastic card to run against Gardy/Sylveon since Magical Ribbon usually leaves me at 7 to 8 cards in hand at the end of set up turns.
I think Gardevoir GX/Sylveon GX will die again when Stakataka GX and Genesect GX hit the field, but it'll depend on consistency at that point. Plea GX is still a thing that can slow down engines like Magnezone, and Zoroark GX is a very very viable back up attacker in steel match ups.
Others have already covered the topic of Psychic attackers so I don't think I need to respond there.
