IMO, the three factors are salary, patience, and overall.
The player has an idea of what he should be paid based on his overall. If his salary is higher and his patience is pretty high, he'll most likely* accept the option. The lower his salary and patience are, the more likely he is to decline the option.
*Edited....that's what I should have said. There's obviously a chance that any player will accept an option or decline one. I think those three factors all modify that chance.
8/26/2010 4:31 PM (edited)