I have both CR books as well. (I also have both SC books from the providers)
The following is solely based on my personal experience:Powerscore CR is a bit more comprehensive in terms of detailing out all the types of questions and the techniques used to tackle each.
MGMAT CR, however, has a good discussion about T-diagramming (if you think this style works for you). I, for one, don't like writing things down for CR and RC questions, so this strategy doesn't work well for me.
MGMAT SC > Powerscore SC because of similiar reasons described above. I think
MGMAT SC does a better job being extremely thorough -- it can work for or against you (as what the prior post had indicated). I think it's always nice to have something VERY comprehensive so you at least have a source to refer to.
hope that helps