I always measure to where I think my sit bones are on the saddle. The nose will be fine if the saddle are the same profile. But perhaps the rear of the saddle might be more reliable place to measure to as the difference from where my sit bones are to the rear is probably more consistent than to the nose of various saddle profiles.

Also, when you say to the handle bars, that works for a flat bar, but on anything else, I'd measure where you actually keep your hands. For those that normally keep their hands on the horizontal part of a drop bar, then something is set up wrong or the frame is the wrong size.