If you're willing to fund overhead and give up the direct-to-recipient portion, you "should" contribute to PIH because nonprofits have a much easier time covering their program costs compared to overhead costs. Nobody wants to contribute to office supplies or fundraising costs, they're not sexy, even if necessary.

Of course, you should also support Watsi because as they succeed and drive a ton of extra contributions toward program-costs-only, even if there isn't enough existing overhead covered, there "should" be strategic donors who see this happening and decide to fund it.

This is all assuming Watsi's average partner is interchangeable with PIH, along with the treatments you'd be funding, which of course they aren't. Based on Chase's comment on Bageshwori, it may be very different-- it sounds like by directly funding PIH you'd be contributing to basic (though still potentially lifesaving) care through PIH, whereas with Watsi-via-PIH you have the option of (and often are?) contributing to more difficult, expensive, and perhaps otherwise-even-more-unavailable care.

If you're feeling generous, support both :)

(PIH spends a remarkably high 94% of its donations on program expenses, fyi: http://www.charitynavigator.org/index.cfm?bay=search.summary..., though there's long been a philanthropy-wide consensus that over-focusing on overhead is common and unhelpful: http://blog.givewell.org/2009/12/01/the-worst-way-to-pick-a-...)