Tough one.
In your hypothetical, is CCW still allowed? If so, that becomes a major factor, if I only get one choice.
For me, either Kahr PM9 or Kahr P45/Kimber 3" 1911 Ultra Carry. The PM9 is (for me) the ultimate balance between power, weight and concealability. The 45s are confidence-inspiring but larger, heavier (and more expensive to feed) but still very compact for a 45 acp.
If CCW is not a factor, then a 4" K-or-L-frame S&W. M-19, M-66, M586/686 come to mind.