I really like how the giant snakehead looks. It's really cool while at the same time it slightly unsettles me too!
The sharks also look like IKEA sharks since they're blue and how couldn't I possibly love that.
In practical terms, my favorite is probably the football fish. I like deep sea creatures like that and it looks striking compared to the rest of the fish you can catch. It's also not too big to look nice if displayed in a home while not being too small either.
I really like the soft-shelled turtle and I wanted to display one in one of my mayors' houses, but I was disappointed to see how absolutely tiny their tank is. I just sort of feel bad looking at them not being able to swim around and I couldn't justify keeping it as a pet because of it.
The goldfish is pretty alright due to their nice looking fish tank. I also like how the angelfish, barred knifejaw, frog, and piranha look and I like how the piranha will bump against the glass trying to get at the nearest person.
A lot of the others I like are way too big to display in houses while still looking nice, like the coelacanth, dorado, oarfish, and Shark.