I don't know the 18-200mm BUT assuming you don't plan to sell these images to National Geo or wherever (
) I'd take that. More tele reach and a decent wide angle with no lens changing.
It depends on how flexible and reactive you want to be. If you feel sleuth-like then go for the single lens. If you are like me, if you take 2 or 3 lenses, you'll be mucking about with lenses JUST as ops unfold.
The tele will also allow you to pry a bit.
(Assuming you can do that.)
If you see people or a person you want to nab. Aim on something (anything) about 90° off target. And then casually pan ... stop and click on target ...and then keep panning as if nothing happened. Look up at the sky...hum a tune. Casual like.