It is a matter of how alluring a woman's figure is in the eye of a beholding man, I'd say (speaking from a man's point of view) A good figure looks good in either pants - that show off her body lines - or a figure-hugging dress. The wolf-whistle factor is there in either case.
On the other hand, if a woman is grossly overweight she'd be far better off in a loose-fitting dress than trying to wear jeans. A good, well cut dress of the right fit can work wonders here.
But I think most people know this - except, perhaps, those who do not see themselves as objectively as they perhaps could.