An important immigration policy question is to identify the best criteria to select among potential migrants. At least two methodological problems arise: the host country's immigration policy regime endogeneity, and immigrants' unobserved heterogeneity. To address the first problem, we focus in a country with an unprecedented immigration boom that lets immigrants freely into a country: Spain. To address the second problem, we focus on a large and homogenous group of immigrants: Moroccans. Using the 2007 Encuesta Nacional de Immigración (ENI), we find that, even when focusing on a very homogenous group of migrants (Moroccans) who tend to be low-skilled, and after controlling for migrants' self-selection with employment history prior to and at arrival, family-based immigrants are less likely to work than their labor-based counterparts both at arrival and ten years later. Our Heckman-corrected estimates highlight that there are no monthly earnings differences by reason of arrival, and that failure to correct for labor force participation strongly biases these results.