I think the safest thing to say about little ones is awww cute, and pretty color.
I have enough trouble judging big guys, but foals are really hard, being that they are all legs and bendy soft joints. This little guy currently looks all head and legs, at the expense of his neck, but who knows what he will mature to. I'm still waiting for Angel to produce a decent neck, I'm sure she will at some time.
What do I look for, well I've never had to select a baby at that age, and having raised a few foals at home here I hope I never have to, because they go through so many stages.