my personal favorite are turquoise rainbows. I have two, they are at least 6 years old by now. I started them in a skinny and tall 30 gallon hexagon, they swam vertically but swam a lot. Now they are in a 46 gallon long and they swim horizontally and vertically and all over. They are a male/female pair and so the male flashes his nose colors all the time at her and she subtly puts him in check when she isn't in the mood to be wooed. They constantly get in the way when im trying to take pictures of plants, and they are all over me when I do a water change. mine are I would say full grown at 3-4" so not the biggest of the rainbows I would say but they were happy in any tank ive had them in.