Well, I assume since this is tagged as "PTCGO", the "meta" is that of the Theme Format.
I don't know how the two latest Theme Decks will shift things, but here are the ones I think are still worth playing.
Exceptions arise from some older ones being the best options for a new player grinding out a particular challenge. I won't be listing those, at least not yet (
maybe later).
Ignore anything from prior to Sun & Moon. There might be a few gems buried there, and some you may want to get for cards that help in Expanded, but the powers-that-be seem to be taking Theme Decks a little more seriously, to the point they might finally deserve the title "Starter" deck.
Destruction Fang
Clanging Thunder
Mach Strike
Imperial Command
Tropical Takedown
Twilight Rogue
Leaf Charge
Hydro Fury
Storm Caller
Blazing Volcano
Pre-Lost Thunder the Mach Strike deck was probably the best grinding choice. It tends to either win or lose
quickly. It was the best deck when it released, but it has slowly lost ground as newer decks released (as one would expect). Nowadays, it is probably a little overhyped; still a very good deck, but given how often it misfires compared to more recent decks, I think some folks just rememer all the games where an opponent opens with Gible and quickly Evolves into Gabite and then Garchomp but forgets all the games the deck fails to field a Garchomp quickly, or gets Garchomp but opponent sets up so quickly as well that Garchomp doesn't last long.
Personally, I'm fond of Topical Takedown, but my "less than a dozen games
combined" testing of St0rm Callerand Blazing Volcano have impressed. Storm Caller has 10 Supporters while Blaziking Volcano has 12! Hydro Fury and Leaf Charge also each have 10. I only count eight a piece in Tropical Takedown and Twilight Rogue. IMperial Command has nine while Mach Strike only has seven! One of the former best decks, Battle Ruler (XY -Fates Collide) only has six Supporters, while "Roaring Heat" (released alongside Sun & Moon) only has four! Four has long been the expected Starter deck amount...