Who you choose is dependent on what your goals are.
Do you want a one year "patch", then Bogut is the best choice. He's played before in a pace and space offense, he doesn't demand heavy minutes, he rebounds, defends, and passes well. He'll be excepting of the celtics system of going small at certain times. If he's healthy, he'd be a decent fit.
Are you looking to obtain a center for the future, then Noel is cheap for this year, and you get to see how he fits in the system for the future, as to should you make him an offer for next year. Young aggressive defender, runs the floor well, defends, and rebounds well. He can defend multiple positions.
Asik is expensive and a poor fit.
Lopez is too expensive, but he fits the system. Not a great rebounder, but he stretches the floor well. But he would limit the signing of a future star because of his contract.
Nurkic is interesting... young, strong, and talented but does he fit the system? Right now he has a good contract, and is prime to keep and develop. If he could be gotten reasonably...