Really depends on the kid and the teachers. For math whizzes, BC Calc isn’t going to be as hard as something which requires tons of reading. People in STEM often perceive that math and science are the most difficult subject but really any course can be, if given the right teacher and adding in a kid who has trouble in the subject area. I do, however, agree that the time commitment is a factor ( it’s not a factor for being difficult but it is a factor for kids who already have too much on their plates).
I would look at the College board ratings ( they rate how many people got which scores in each subject area) then factor in your own strengths. I looked at this once and was surprised that some of the esoteric languages had very low scores. Have you considered taking some of these classes online? Honestly, it seems like APs are a distraction to real, deep learning in subjects which students have an interest. Instead of following a passion, they are following a syllabus for a test which means little later in life. Just my opinion. I know students need them to get into the best schools but they don’t seem to serve the kids very well.