i got 5 praecox rainbowfish as an early Christmas gift, and they are my current favorites (it changes every week or so, i admit).
they are a gorgeous electric blue with scarlet fins, and they school beautifully. they are really zippy and add activity to the tank, but they are completely peaceful. they have a pretty shape but are so narrow that they disappear when they turn sideways. it is like they are 2-dimensional! i love having a larger bright blue school as a counterpoint to my school of neon tetras. can you tell i love blue fish?
bettas are my overall favorite for personality and intelligence. they recognize you and respond almost like a puppy. mine loves to be petted and to chase my finger.