I would say my rays. I've owned many fish but the joy to see a ray in your tank swimming freely and seeing their smile on their belly( their mouth lol) is so relaxing.
My biggest headache fish are arowana constantly worrying about it jumping and etc
I was expecting a lot of people to say arowana they are pretty relaxing the way they just cruise the top wasn't aware of how problematic they are? Maybe I should turn this thread into Most Tranquil and MOst Annoying.
For me out of all I've kept it's Angels and Discus haven't kept fancy Goldfish or Rays though, I realized after looking at my tanks all the fish I have are pretty crazy currently have guppies, tiger barbs, and flowerhorns none really relaxing.
Most Annoying I've kept have to be Bala Sharks Infamous for be skittish and jumping, horrible fish IMO