Jesus you shouldn't even have to ask this question. Facebook all the way. It not only carries more weight, but you're more likely to work with new cutting edge tech. Remember Palantir is mainly a Java shop in the finance and gov sectors, while Facebook is the "next big thing", just like Google was.
Among highly-skilled engineers in the valley (i.e. the ones who'd be working at FaceBook/Palantir/Google), Palantir is at least as highly regarded as FaceBook, and quite possibly moreso. They aren't all that well-known outside of the valley, because they do enterprise software, but the caliber of their engineering team is pretty legendary.
And that is exactly the reason he should go to Facebook instead. I never questioned Palantir's engineers - I don't get why you make such assumption. The simple truth is that for a person starting out it looks insanely better to have Facebook in your CV instead of Palantir (generally speaking off course). If he was an experienced engineer and was offered a similar jobs on both companies, then that is a different story altogether. Facebook will have more impact on whatever this young man does next, anywhere he does it, be it in the valley, or in a too hot third world country.
Really if you want to get into Palantir's industry, there is, of course, no better choice. But if you want to get your feet through the door, there's no better option than Facebook right now, and that has nothing to do with the quality of either engineering teams.
