I dunno what upside Cain has, he is who he is. Bumgarner is scary, with terrible late season work to the point where the Giants would rather throw Zito than him
Darvish is intriguing, but if we are talking upside, Dickey really has the most, and all he would have to do is repeat or come close to repeating to realize it. CC was my choice because he is a safe bet, I'd rather have Dickey than a lot of other pitchers if we are just talking about potential and upside.
A lot of this is gut feeling so I don't have much to back what I am saying BUT I worry about CC as he is over that age 32 where you start seeing a decline in both health and production. It might end up being a year early but I would rather trade him now and get close to full price for him and be a year late than hold on to him and see a season like Halladay happen to him. It is just a matter of time because we know it will happen we just don't know when.
Dickey is just different. No one understands how is he is doing what he is doing and I would rather not touch him. He is well into that age group where production and health will always be a concern even though his stuff is easier on the arm. The real problem is that knuckballers aren't this successful so you have to wonder how long he can keep it up.
I still think Cain has upside. He has yet to be a 20 game winner or throw 200 K and I think both are possible for him. He might not do it but I think he is at that age where we see a lot of pitchers move into the Ace grouping and he has had a lot of success that says he could take that step. Bumgarner has some worries but he is also very young and has had a ton of success in the first couple years. He could easily be a top 10 guy in the next 2-3 years. I think Darvish has the most upside of all three. First year, he already has a 200K season. He had a lot of growing pains this year but he worked through them and I wouldn't be surprised if he was a perennial top 10 pitcher for years to come.