I know they're somewhat common, but I really do love my mollies. They've got great personalities, they're hilarious to watch. They're also ridiculously friendly.
Now, I don't know about ALL Raphael cats, but I love *my* Raphael cat. His name is Zorb. He's hilariously grumpy. I rarely see him. But I feed him pellets. I usually put them just outside his hidey pipe by hand because otherwise the mollies will steal them. He comes out and grabs them. We have an understanding.
So after the mollies, I'd have to put cory cats. The're just great little guys who do their own thing around the tank. I like the albinos and pandas the best, but that may be because I have a thing for black and white.