During the LSH's existence, Ultra Boy has garnered his own little following. When the big three of Superboy, Mon-el and Ultra Boy would be together, it always seemed as though Jo would have more of an appeal than the other two.
I also believe he has been spotlighted or been the standout of various story arcs more than most other team members. I've also noticed that the brunette guys seem to be favored over everyone else. Karate Kid, Leviathan, Timber Wolf, Invisible Kid, Star Boy. Hmmmm....a pattern.
In your own opinion, why is that? What is it about Jo that's more appealing than, say, Star Boy or Element Lad? Is it his powers? Or the fact that he can use them only one at a time? His origin? What? WHAT?!? I gotta know!!!!!!