Which major is most beneficial towards becoming an Anesthesiologist?

When wanting to attend medical school, keep in mind that they typically want young candidates with a high Undergraduate GPA, like a 3.75 or higher, and high scores on the MCAT (medical college admissions test). You do NOT have to have an Undergraduate degree in science. Many students have other degrees to keep a high GPA. Then they take the additional Undergraduate courses required by the medical school. Be sure to go to the website of each medical school to see their Undergraduate course requirements. Good medical schools post the GPA, major, and undergrad degree of the latest students accepted.

It is advisable to pick an undergraduate degree that you love, because medical school is extremely competitive; so just in case you do not get accepted, you have a degree in a career that you can pursue and be happy.

You can also study for the MCAT early in your freshman and sophomore years in college to ensure you will make a good score.

Khan Academy has a wonderful, FREE review.

https://www.khanacademy.org/test-prep/mcat

There may also be medical school preparatory programs at your university or in your state that help prepare qualified students for medical school. 

When Googling, use a reputable source, such as US News and World Report.

https://www.usnews.com/best-graduate-schools/top-medical-schools