I would vote them all. They could all be starters for Juve.
Legro is just as good as Ferrara at this point in Ferrara's Career.
Maresca is as good as Tacchi and his Summer performance suggests he may even have more offensive push to add to the team.
Appiah couldn't replace Davids. He may not have the technique and physical power/work rate, but he's better rounded as a footballer because he can make better passes.
Miccoli could be a starter, because Del Piero's form fluctuates so he could start while DP gets his calcio-mojo back. He could even replace Camo if Lippi plays 4-2-3-1. Although Miccoli hasn't settled with this formation, he could still replace Camo who showed last season that he could also have his "off-periods" like DP.