CS 61B is likely to be the most familiar to students who have had AP CS A in high school (or introductory programming and data structures at many community colleges), since it contains that material plus additional or more difficult material along similar lines. Course home page is at http://fa20.datastructur.es/ .
CS 61A includes topics that many other introductory CS courses do not cover; see the course home page at https://cs61a.org/ .
CS 70 is a discrete math course. Some students find it difficult because it is unlike the math that they have previously encountered. Course home page is at https://www.eecs70.org/ .