Pokémon Park question

[Hoyas]

Pokémon Park stadium says: Once during each of his or her turns, whenever a player attaches an Energy card from his or her hand to 1 of his or her Benched Pokémon, he or she removes 1 damage counter, if any, from that Pokémon.

I attach a Rainbow energy to full HP Pokemon. Which activates first: Rainbow energy's damage effect or Pokemon Park's healing effect?

 

[BJJ763]

Since both effects trigger simultaneously, the owner of the Pokémon gets to decide the order.
The owner could opt to put a damage counter from Rainbow Energy and then remove 1 damage counter from Pokémon Park.
Or the owner could remove a damage counter from Pokémon Park and then place a damage counter from Rainbow Energy.