Who is really heartless?

I find it odd that Nobodies (Particularly Organization XIII) seem to come off as more heartless than the actual heartless. Apart from Xehanort's heartless ("Ansem") heartless seem to be just goofy looking creatures that seem to just instinctively spread darkness where and whenever possible. Also any Emblem Heartless has inside them a captive heart. So they're heartless...that have a heart inside them? This is something I've just always noticed. What do you think?