Geez you ask a difficult question.
I can't make up my mind. Nank is not a huge ruck, but he can compete and he is great around the ground. Soldo can compete slightly better at ruck contests, is offering a little more around the ground than he used to, but clearly less than Nank. Chol is not so competitive in the ruck but serviceable as a relief ruck and great around the ground.
Looking at all of that I suppose I would go for Nank and Chol but we would miss Soldo now with his improvement.
Players like Grundy are freaks, he is 202cm (6'8") and yet he can run and is mobile. Amazing. Not much taller than Nank or Chol, maybe 3cm or 1 and a quarter inches, and you can't just let a weapon like that free to do what he likes. Soldo was very good against Grundy and he makes a very good case to stay in the side.
DS