I personally don't have a preference between them. Portra 160 was developed to be "neutral" for color, while Portra 400 was developed to make colors "pop" more. Ektar 100 is supposed to give even more contrast and saturation to the color palette.
I would use Portra 160 in a heartbeat for photographing a child. And if available light is a problem, there is also Portra 800, which can be underexposed with good results. I think the Brothers Wright did a test of it in 2010.