I was pondering over what classes I should be taking during junior and senior year. My choices are to either (1) take 6 APs junior year and 4 as a senior or (2) take 5 APs in junior and senior year.
Here is my set schedule for Junior year’
AP English Language and Composition
AP Calculus BC
AP Physics
AP Art History
AP Psychology
Spanish 4
Schedule for Senior Year
AP English Literature and Composition
AP Statistics
Anatomy and Physiology
AP Economics and AP Political Science
AP Spanish
Should I take AP Music Theory as a junior or a senior? How difficult are these AP classes?
Thanks for your feedback! 
The difficulty of the classes will be dependent upon the teachers at your school; there is no standard. You should ask students currently taking those classes. The two wildcards are Art History and Music Theory as part of the difficulty will be based upon previous background in art/music.
As for when to take, it’s probably a toss-up. One thing to keep in mind, however, is that hidden class that you will have Fall semester of senior year: College Apps and Essays. People always seem to underestimate how much time these will take.
Take option 3. Lighten up your senior year and don’t overwhelm yourself junior year. Do 5 APs and a junior and 4 APs as a senior.