I see all these comments in the vein of 'why should you force people to work in the mines and not get to love their child' and I wonder if any of these people have ever had toddlers. I love my kid, and love spending time with her. But she really likes daycare (and now school). Not only does she get better socialization than me taking her to the park for 2 hours, but she learns skills that I wouldn't be consistent about teaching. It turns out, being taught by people who have years of practice and degrees in childcare is a pretty good idea!
We did Prek-4 at our public school and you could immediately tell the difference between the daycare kids, the nanny kids, and the home-parent kids. The daycare kids were much more prepared and able to cope, and this is at a school where parental involvement was quite high. I don't think the different approaches are universally better or worse, but it's clear to me that the quality of the daycare and the parent matters a lot more than which one you choose.