You want to be both precise and controversial. Sometimes it's wise to start with something else, the better to grab the reader's attention. But you should get to your thesis statement pretty quickly, so your reader knows where you're going. That versus Which. According to the more quibbling self-styled grammar experts, that is restrictive, while which is not.
Many grammarians insist on a distinction without any historical justification.
Many of the best writers in the language couldn't tell you the difference between them, while many of the worst think they know. If the subtle difference between the two confuses you, use whatever sounds right. Other matters are more worthy of your attention. And the answer is the one that is used most often. There are two rules of thumb you can keep in mind.