CDR: Some are longer some are on par. CDR is quite heavy on inference/tone questions with sometimes topics not related to sciences - a lot of history type of passages. Rather, it is still a good practice. On real DAT, you will probably see all 3 science related passages, at least 2 though.
Topscore: The most realistic representative of DAT RC section as far as topics covered, the length of the passages, and the difficulty of the questions.