I may be limiting my judgment to the scope of my own experience, but I'm fairly certain that 9th and 10th graders begin their high school career by all taking approximately the same generalist classes. Junior year is probably the first time most high school students start to take advantage of AP, IB, and honors-level classes.

That said, you should choose your classes wisely. If you're a honors-level student, then make sure to start choosing an array of AP classes. If you're maybe a lower-level student, then try to get in a few APs to show colleges that you're aiming higher.

Also, if your school offers IB, you should really discuss with your school's IB program director or your counselor to see if IB is right for you. When considering a decision between AP, IB, or both, you should think about what kind of workload you can handle and what kind of credit you're looking to get by the time you reach college.

Usually, Junior year is when students start to take AP classes. You should try to take as many as you can handle. Doing well on AP classes and getting 5s are a great way to show colleges you can handle college material.