The debate between free will and determinism is a hotly contested one, and taking a stand on it is important, as it affects how you view the world, the people around you, and how culpable they are for their actions.

• Free Will: The philosophy of free will posits that humans are free to make choices - that when we make decisions, we could have done otherwise. In favor of this viewpoint, well, we certainly feel like we're free, and it's easy to imagine that I might have chosen blue for the title of this website rather than green.
• Determinism: Determinism, in contrast, states that the physical world follows some physical laws that always act in the same way, and that because humans are physical objects, we are subject to those same laws. There is no room for free will in this picture - the future is a necessary consquence of the past. Our choices could not really have happened any other way, but the causes of those choices is hidden from view.
• Compatibilism: Maybe these two viewpoints aren't actually at odds, and it is possible to have both free will and a determinsitic Universe. This is called compatibilism, and it usuall revolves around redefining "free will" to mean that an agent had the potential to make other choices, even if it was already determined that they would not.

I believe hard determinism is the true approach here. About the only argument going for free will is the fact that we feel free to make our own choices, but how we feel about reality is generally irrelevant to what reality is actually like. In contrast, the vast majority evidence we have examined so far indicates that the Universe is bound by physical laws, and there is no reason to suppose humans are exempt (without invoking souls or other such ad-hoc assumptions). While it's true that we don't know that these laws are certain to be true in all circumstances, the majority of evidence is on their side; and even if the Universe were not governed by physical laws, that does not imply free will. For example, suppose quantum events are random (which is not a consensus among physicists); this does not support free will, because we still have no control over the results of these quantum events. I also feel that compatibilism is essentially a cop-out answer for people who are uncomfortable with determinism but have no cogent arguments against it. By redefining free will to be essentially meaningless, they become technically correct without actually saying anything meaningful. While I've not yet seen a strong argument in favor of free will, it is often practical to behave as though we have free will, as it is generally necessary for moral culpability to exist, and having an existential crisis 24/7 will tend to impede on productivity.