My favorite are the neons, i have had them around the house for years and i still love them.... At one point there were in with some goldfish with a tank we brought second hand and they all seem happy, VERY ODD
KathyM gave me some penguins a while back, and I think they're very nice too. Really dont like my blue tetras, they looked nice initially but have now all faded as they've grown, healthy enough but very plain.
Oh and the columbian's Kathy gave me too, they're lovely.