Last month, we asked you, in a world of underground monsters, which creatures (aliens count) would you want fighting on your side? Congrats to Robert Bertrand! He wins a signed copy of Jekyll & Hyde, Inc.
I'm guessing it would be a cop out to say "man" since we all know very well the levels of depravity humans themselves can reach without even trying that hard. Barring humanity I would choose the vampires in Larry Correia's Monster Hunter Series. They have all the potential for destruction and suffering that humans have with 100% less soul. A dangerous ally not even slightly mildly grounded in morality or ethics would be useful in a pinch. I'd personally choose the Master Vampire version of Elon Musk for entertainment value alone.