My experience (as is most others familiar with the line) is that they all sound pretty much exactly the same with the exception of bass extension and linearity in larger rooms.
Though, were I to pick just one, it would be the SC-5.
That one was the only one to use a slightly smaller and more dynamic midrange cone. To my ear, this meant better midrange clarity and tone. But it still retained the ability to play 20Hz with power, even in large rooms.
Case in point..... In my party days I used to come home from the clubs and crank up some 20Hz sine waves late at night. It was juvenile fun hearing my apartment neighbors talk about the minor "earthquake" we experience the night before.