Throughout this format, we have had a notorious "big three" consisting of Dino Rabbit, Wind-Up, and Inzektor. Everyone knew what decks were being discussed when someone simply said "the big three". Then came YCS Long Beach, where Heroes and Dark World became "somewhere up there" along with the big three. I personally felt that Wind-Up deserved to be dropped from its status, but for the most part, everyone still considered the big three to still be those decks. The next US YCS, Dallas, and the European one, Tolouse, gave rise to Chaos Dragons. Forget Nizar Sarhan's win with Dino, everyone was talking about Dragons. This was a deck that seemed to come out of left field, where many veteran dragon duelists such as Dragon Duelist Girl and Rich "Draigun" Clarke initially dismissed the new archetype and claimed regular Disaster variants were better. At the YCS, Alexander Reed and most of his friends that used the same deck (for the most part) did exceptionally well at Dallas, so obviously they had stumbled onto something.
Fast forward to last weekend's YCS, Chicago, and we can see that Chaos Dragon took just as many spots in the top 32 as Dino Rabbit at 9 a piece, with Inzektor taking 8 total spots. Priority or no, both Rabbit and Dragons made a big appearance and impact. Famous players such as Allen C Pennington and Cesar Gonzalez ran Dragons and did well throughout Swiss. I was personally rooting for Allen to win, but he has made it well known on DGz that he got sacked hard in his top 32 match. I believe there were only 2 Wind-Up decks that made it into the top 32, and only very few of everything else. When Rabbit, Dragons, and Inzektor account for 26 spots, well there's not room for much else. It's crazy to think how an event or two can change the meta completely.
The release of GAOV may also cause a shift in the top tier decks and bring about many questions that I'm currently curious about: will Hieratics prove to be a viable deck in the TCG? Will Ladybug give Inzektors the extra "oomph" they need to win a YCS? What role will Cardcar D have in all of this? Do Evols have enough support now to live up to their hype? Meta-shifts like these are exciting and yet bring up so many questions where the answers are almost always difficult to find. In most cases, with the top players being very secretive about what they find at times like these, the only kind of answer one can find is by testing or just simply waiting it out for YCS results. Those that are able to put in the time to come up with their own conclusions about formats are usually always "ahead of the game", but then again not everyone has the time to put much into testing.
To conclude, I just want to say that if you're one of those (like me) that aren't able to put much time into testing, and you're going into some event, all you can do is go with what you're comfortable with. It also helps to spend some time researching what others have found, and go with your gut/theory-oh. Anticipating what others are playing is also a big factor regardless of where you play.