<p>This totally depends on which schools you're applying to and when. Every top school probably tries to have a decent amount of people who fit into each of these categories, if possible. That said, some top schools have more money than others, and I'm assuming that, when you say legacy, you mean legacy who donates to the school, since that certainly makes a difference and, to my knowledge, is a lot of the reason this counts. At Harvard, which has the biggest endowment of all non-profit organizations, let alone colleges, I would guess that something like legacy would mean a whole lot less. The recently closed Antioch had an endowment of about $36mil and basically had to admit legacies whereas Grinnell College, with a similar student size but the largest endowment for LACs, had 1.5bil in 2006. They can clearly be a lot more picky in this respect. </p>
<p>That said, at a top school with a hefty endowment (basically Harvard type), I expect the following groups to be the most difficult to fill, and thus the most helpful in admissions:</p>
<ol>
<li> URM Native American (obviously w/ decent stats) I feel like, in general, the Native American perspective is soo seldom represented at schools, and in general, the most unique. Part of the purpose of having diversity is to expand the whole student body's horizons and bring in new perspectives. I go to a very diverse, metropolitan public high school (roughly 30%hispanic, 30%black, 30%white and 10%asian). I've met only a handful of Native Americans (who grew up on reservations) and their insight and experiences always opened my mind.<br></li>
<li> low income and first-generation student (though it likely depends on race and other factors)</li>
<li> URM black/hispanic</li>
<li> professionally published work, though it depends on where. If someone has had an article published in the Post or Times, or a poem or story published in the New Yorker, that definitely jumps to the top of the list. The circulation of the publication, along with whether the applicant wrote it by themselves (versus with a researcher as part of a project that the student only helped out with) makes a big difference.<br></li>
<li> Disability- again, relative. For me, having had cancer recently definitely helped as a hook, but I doubt that it would've been helpful had any number of small things been different. Assuming that the disability is one where it's the first thing any given person on the street notices about a person, I'd rank it 5th.<br></li>
<li> born in exotic country, depending on whether they're an int'l student (generally taken as a plus at schools, and int'l students generally have to pay their own way), which countries they've lived in (If they spent half of their life in third-world nations, seeing poverty/war firsthand on a regular basis, they clearly bring a more unique perspective and have likely been more challenged than someone who switched between wealthy western European countries)
After that, these all seem like things you would want to mention and that would pretty much function as relatively strong ECs, but not that would be hooks.</li>
</ol>