my favorite has been unattainable, and that is the rainbow ( Nematobrycon lacortei )
I’ve tried multiple times, and ended up with many nice fish, but never a true lacortei
I also love the Cardinals, ( Paracheirodon axelrodi ) I try to maintain about a dozen in my tank
as well as the Rummy’s ( Hemigrammus rhodostomus ) and cousins, which I also try to maintain around a dozen
the “other” Emperor ( Nematobrycon palmeri ) I’ve always liked, as they are easy to sex, the males have blue eyes, and the females have green, and these were most often sent by mistake when I ordered the lacortei, so I have a boatload of them in my south American Tetra tank, by default…
and as a bonus, while they are not in your face pretty, I really like the sailfin tetra ( Crenchuchos spilurus ) for their unique habits, and unique lifestyle… I currently have 5 of these rarer in the hobby fish