The larger species, such as the tomato clown, fire clown and sebae clown, are somewhat hardier. My choice is the tomato clown. This species maintains its color well in captvity and seems to do fine without an anemone to live in. They do grow somewhat larger than other clowns, sometimes exceeding 4 inches. Even at that size, however, they do not exhibit significant territorial aggression.
Cardinalfish are choice number four.
Although lacking stunning colors, they are hardy and totally without aggression. They generally grow to about 3 inches. When first introduced into your aquarium, leave the lights off to prevent the fish from going into shock. The one advantage the pajama has is that it doesn't seem to hide as much as the other species. There are apparently two species of pajama, one having better defined colors than the other.