This list is a bit shorter than the last few, but all of these cards are solid additions to any deck.
Anyway, here’s the list:
Great Ball (Pre-BW)
Blaine8/10
Great Ball (like Nest Ball) is great for getting an early Pokemon onto your bench and avoid being “donked”. It can be cut in decks where you want Pokemon in your hand to discard or play with a “from hand” ability.
Tony9/10
The Stormfront printing is the preferred version, but the printing from the ex-era is just as good in most decks. The post-BW printings have a significantly different effect.
The best “ball” effect in the format, since there will never be a 2nd Luxury Ball in your discard pile. This is like ACE SPEC Master Ball without using your ACE SPEC.
Tony10/10
The downside of this card is completely moot in Partner Battles. It searches for any Pokémon [except LV.X], and puts it in your hand.
Pokémon Retriever
Blaine7/10
In a singleton format, these “revive” effects are great. I usually fit either a Rescue Stretcher or Pokemon Retriever in every deck (sometimes both!).
Tony8/10
Recovering ANY Pokémon card to hand is a pretty powerful effect, so you’re going to choose the first option most of the time, but the second option is not bad either.
Two copies of this go in almost every one of my decks, usually only limited by how many copies I own. A neat trick is using a Skyla to grab the 2nd copy while you have one in hand, then get any two cards from your deck!
Tony8/10
This card is one of the few cards that you can and also want to play 2 of in a Partner Battles deck. It’s not as difficult as you might think to get both in your hand.
Format Staples - Part 4: Trainer Cards - A Few We Missed Along The Way 
Format Staples - Part 2: Trainer Cards - Base Set through Skyridge