Would you rather be locked in a room with Voldemort or Bellatrix?
What a question... I would honestly prefer neither but if I had to pick I'd go for:
Yep, Voldemort. Now I know he's the ULTIMATE baddy, but Bellatrix was the one that really seemed to love that cruciatus curse way more than any other Death Eater. I really wouldn't fancy being locked in a room with her. Plus she killed Sirius :(. I'd want to try and learn more about Tom Riddle's past as well and attempt to pick his brain... and hope he doesn't get an itch in his wand hand for the ol Avada Kedavra.