Top 3 worst players we ever had
Easily
I can't talk about "ever", but for the last 25 years, he's the worst one.
The list of players who performed terribly for Juve in this time period is not that big. We had players who were expected to do well but it didn't click for them and they got at most 10-15 matches (Oliseh, Esnaider, O'Neill, Salas, Bojinov). We had players who were here for a season or two and sucked really bad (Boumsong, Mirkovic, Poulsen, Criscito, Almiron, Tiago, Grosso, Jorge Martinez, Elia, Hernanes, Emre Can). We had players who had a terrible season (Legrottaglie when he first joined). We had guys who should have never been here in the first place, yet they collected a lot of games in a particular season or two (De Ceglie, Zenoni, De Sciglio, Ruben Olivera, Rincon, Giannichedda, Peluso, Blasi, Nocerino, Molinaro, Sturaro, perhaps even Grygera can be included here). We had disappointments like Diego and Krasic...
Then we have the cancers. Players who were expected to do well or great, but they showed serie C quality and were harming the team in many ways: Amauri from 2009 on; Felipe Melo who I still insist was not right in his head; Aquilani, Isla.
And in the end, the mothers of all cancers, the worst of the worst: Marco Motta, Daniele Rugani, and Federico Bernardeschi. Berna easily beats the other two.