Cards aren't usually what is determined good for any format; decks, their consistency, and their synergy are what is typically judged as good or not. However, there are some cards that are used more often than others, typically due to certain common or current play-styles within the TGC or how situational (or how non-situational) a card is. :P
For Example, you wouldn't want to use a Blacksmith Card in a deck with no Fire Energy, Zeraora-GX's ability (or the card itself) without Electric Energy, nor a Dome Fossil without Kabuto (and Kabutops). :P
Moreover, there are cards, or moreso things cards do, that are almost always beneficial to add to any deck, which include:
Cards that Draw Cards: Such as Hau and Professor Kukui are always good because drawing more cards gives you a better chance of getting cards you will need now or later on.
Cards that switch your opponent's Pokémon: Such as Pokemon Catcher and Counter Catcher are used because bench manipulation is a great strategy to prevent your opponent from getting out of hand, or forcing them to lose Energy is the process.
Cards that get Cards: Like Great Balls, Professor's Letter, and Pokémon similar to Kangaskhan that can get energy faster, get Pokémon/evolution cards faster, or fill your bench while packing a punch.
Cards that get Cards from the Discard Pile: Like Energy Retrieval, Pal Pad, and Lusamine are useful because using something more than 4 times is valuable, and getting energy back may be vital, especially if you have attacks that Discard Energy.
As for Pokémon, you want to use things that won't be a liability, and have only less Stage 2 than Stage 1, and less Stage 1 than Basic. You should also have at least 1 GX/EX so that you can effectively cripple or Kill opposing GX/EX without losing as many Pokémon. :P
Source: EXP
Hope I helped!
