Just wondering which one is the easier and how can I best prepare?
The best way to figure out which test is best for you is to take practice tests for each one. They are slightly different and you may find that the ACT suits you because there are many more practice exams (SAT changed its structure recently).
SAT Practice exams: https://collegereadiness.collegeboard.org/sat/practice/full-length-practice-tests
ACT Practice exams: https://blog.prepscholar.com/complete-official-act-practice-tests-free-links