This is not a sarcastic answer, but the best have been those who have reached the quarters. In that I mean, no surprises so far.
Spain beat Mali in the group for example, but Mali played with 10 men most of that game. So I'm not sure if in an even game that there would be much difference.
Inside this tournament itself
-Argentina have looked a little stronger than Brazil (while Brazil won the recent U17 SA Cup
-Spain have looked stronger than Germany (while Germany won the recent U17 Euro Cup)
-Mali have looked stronger than Senegal (while Senegal won the recent U17 African Cup).
My guess is winner comes from Spain/Brazil side of draw with Mali and France having a live chance on the other side.