Hey Pojo! I'm going to be doing a rating of all Stadium cards from Gym Heroes.

No Removal Gym Stadium Card
card 103/132 Rare
This card stays in play when you play it.  Discard this card if another Stadium card comes into play. A player must discard 2 cards from his or her hand in order to play an Energy Removal or Super Energy Removal card.           

This card is really good, as long as you have no ERs in your deck.
Rating:9.5(would be 10 if it didn't stop YOU also from playing ERs)
            
The Rocket's Training Gym Stadium Card
card 104/132 Rare
This card stays in play when you play it.  Discard this card if another Stadium card comes into play. Each player pays 1 more to retreat his or her Active Pokemon.     

This card is OK. Probably almost every deck should have this card to counter an opponent's Gym card.
Rating:8.0

Cerulean City Gym Stadium Card
card 107/132 Uncommon
This card stays in play when you play it.  Discard this card if another Stadium card comes into play. During each player's turn, that player may choose to discard an Energy card attached to 1 of his or her Pokemon with Erika in its name.  If that player does so, that Pokemon is no longer Asleep, Confused, Paralyzed or Poisoned.

This card is like a Full Heal for Erika's Pokemon. Since it works only with Erika's PKMN, your opponent probably won't be able to take advantage of it.
Rating: 7.0
            
Cerulean City Gym Stadium Card
card 108/132 Uncommon
This card stays in play when you play it.  Discard this card if another Stadium card comes into play. Each player pays 1 less to retreat his or her Pokemon if it has Misty in its name.
Nice card.  Like retreat aid for Misty's PKMN.
Rating:7.5

Pewter City Gym Stadium Card
card 115/132 Uncommon
This card stays in play when you play it.  Discard this card if another Stadium card comes into play. Don't apply Resistance to any attacks made by Pokemon with Brock in their names.
THIS CARD ROCKS!!!!!!!!!!!!
Rating:9.5

Vermilion City Gym Stadium Card
120/132 Uncommon
This card stays in play when you play it.  Discard this card if another Stadium card comes into play. Whenever a player attacks with a Pokemon with Lt. Surge in its name, he or she may flip a coin.  If heads, and if that Pokemon's attack does damage to the Defending Pokemon (after applying Weakness and Resistance), that attack does 10 more damage to the Defending Pokemon.  If tails, the attacking Pokemon does 10 damage to itself in addition to whatever its attack usually does.
This card is like a Digger for Lt. Surge's PKMN. Risky, but OK.
Rating:7.0

Narrow Gym Stadium Card
124/132 Common
This card stays in play when you play it.  Discard this card if another Stadium card comes into play. No player may have more than 4 Pokemon on his or her Bench.  When this card is played, if a player has 5 Pokemon on his or her Bench, that player chooses 1 of them and returns it and all cards attached to it to his or her hand.  (If both players have to return a Pokemon, your opponent returns a Pokemon first)
This is another Stadium every deck should have to counter opponent's Stadiums. Very useful versus Wiggly
Rating:8.25

There's my 2 cents on the Gym Heroes Stadiums!!

If you need help with decks, I can try to help. Send decks and comments to:
wiz8
wiz8@abro.com