The danios I've had experience with are zebra danios and celetial pearl danios. Still have them both. Zebras are very hardy fish and are often used to cycle a new tank (establish a proper nitrogen cycle). I keep a group of 4-5 of them in one of my 55g tanks and enjoy them very much. In a healthy environment, the sheen/color of ZDs is amazing to me. Celestial pearls are real pretty little buggers too. I've got a group of 5-6 of them in my 29g. They're quite tiny. I've had all my danios for 3-4yrs now. I've heard that they can live a long time (proper care of course).