If multiplayer counts, it would be either Imran Zakhaev or Khaled Al-Asad coming after me and I'd be pretty much screwed (seeing as they have military training and equipment).
If multiplayer doesn't count, then I'd be facing the Enclave, Raiders or Super Mutant and, again, would be most assuredly screwed.
If multiplayer doesn't count, then I'd be facing the Enclave, Raiders or Super Mutant and, again, would be most assuredly screwed.