first, we have to determine what "successful" is. if it's getting to work with the best photographers on earth and doing insane crazy artistic campaigns and editorials, then it's probably a pretty good race between a bunch of girls. but if we measure success by world fame and recognition, and by $$$, then well, to be quite frank and absolutely honest. it's basically unarguable that right now, and for the past few years, if someone had to pic, as you requested, "the most successful model in the world" . . .THE most successful model is undeniably Gisele.
She's the only one who is recognized by people like my mother, who know NOTHING about fashion. Her name has become iconized and symbolic of the modern SUPERmodel. she makes craploads of money, waaaaaayyy more than the hottest runway models like hana, julia, eugenia, gemma, all put together. she's the one true supermodel of today.
kate moss and naomi campbell don't count. they are still working models with great campaigns and runway appearances, respectively. but they've been around the block for many many years now, so i don't feel like they're so "in the moment".
its gisele. natalia is not even remotely close. kk is faaarrrr more famous than natalia, whether anyone likes it or not.
i see saturnine had the exact same thought I did at the same moment!!!- 
if you claim gisele is 'the one' for like 8 years then the answer is, 
