Mmmm In my opinion Cait is easier and more safe then Graves, same for Sona instead of Soraka.
I never jungled with Mundo but I would say is not the easiest to gank with.
Singed has a unique mechanic, u are not exactly learning how to play a top bruiser.
I guess I can agree with Karthus even if I think it can be played really badly, and he also has a fair unique way to be played as mid, also u need map awareness.