I have to vote for free will also. Humans have instinct (for example breathing), desire (for example, desire to eat, sleep, have sex), and the ability to reason. Reasoning allows us to override our instinct and desires in situations where we feel that it is necessary. Animals have instinct and desire also, but they don't have the reasoning capacity to make a moral judgement. A cheetah can't for example say, well I'm not going to hunt in this area because I know the population of my prey is starting to get near extinction. The carnivore's intinct and desire will cause it to hunt until there is no food and then go somewhere else. Neither can it make moral judgements such as thinking in fairness it should share some of its hunting territory with another cheetah (That's just a rough example, I'm not a biologist or zoologist). Humans on the other hand suppress desires almost everyday. I desire that cake, but my reasoning tells me that I don't need it. Or I might decide that I will take the consequences of overeating. But it is a decision that is up to me.
Certainly environment and genes are big factors. Genes may give one a predisposition to certain desires or even instincts. Environment gives us the knowledge we can use to reason with. Still I think 90% or more of what happens to me now is really up to me. I can't see placing responsibility on someone or something else.