It’s hard to grade AP courses by difficulty level. There are several variables, including student, teacher, curriculum etc. You can look at average AP scores on College Board’s website to get some idea but even that is not absolute as just because Calculus BC has a high number of test takers getting 4s & 5s, it doesn’t make it easy for everyone as only better able math students take that course, weaker ones move on after Algebra or Pre-Cal, others stop at Calculs AB.
AP Human Geo, APES and AP Psychology are commonly considered easier by many.