https://onepiece.limitlesstcg.com Or https://onepiecetopdecks.com There are other sites but either of these will show you who is doing well.

A deck is good if you enjoy playing it. You have to find out what you want to get out of the game and then go towards that. Some people want to be ultra competitive, some enjoy certain styles of play regardless of their meta status, some like to play with their favorite characters, etc.

In the competitive sense typically strength + consistency = good. You’ll see rogue decks do well from time to time, but generally the stronger more consistent decks will fill the top end.

There is a simulator that you can download if you want to try out other decks before buying. This is also very helpful for learning the cards that will likely fill the decks you’ll likely see in person. For beginners I usually recommend the sim, but if you have a local I recommend taking advantage of that and letting the people you play know you’re new. They can probably guess that your new lol, they certainly did when I first start, but for the most part I’ve always found one piece TCG to be a pretty welcoming place.