M1 is mechanics which can involve a lot of basic physics and calculations.
S2 is essentially interpretation of more stats.
Which of the 2 you would prefer will depend on your personality. If you prefer calculations and figuring things out so even if M1 is harder, you would enjoy it more. If you don't like writing long passages and being wary of using keywords or phrasing, S2 can annoy you.
If on the other hand, you're more of a descriptive person, S2 might be a better choice. The logic used in mechnanics can be a pain if you're not much of a logical thinker.
S2 will also be more useful if you don't intend to study anything related to physics at university e.g. engineering, physics, physical sciences. Stats is commonly used in a number of areas in academia, whereas mechanics is more niched.