Are prehung doors or door blanks easier to install for a beginner?
This would depend on the tools at hand.  If you have the proper chisels and jigs using a blank would be fairly easy, and you would not have to worry about squaring and plumbing the frame.

If you only have a 4' level, a hammer, and some shims hanging a pre-hung door would probably be your best bet.

A third option is if you could find a pre-hung where the hinges would line up with the existing frame, you could simply hang the pre-hung door in the old frame.  This option eliminates almost all the work.

In my opinion, if the existing frame is true I would rather use a blank.  Most pre-hung doors come with really cheap crappy frames (unless you pay extra for a good one), so any time I've used one I ended up building my own frame anyway.