I actually have a post very similar to yours. Posted several months ago.
I personally used the LSAT Trainer and it is a successful book. He is the co-founder of Manhattan prep, so he knows what he is talking about.
I never used the PowerScore books myself, but I have not heard any bad reviews about them thus far. In fact, all of my friends that used PS have increased in their scores, so I am assuming PS successful as well.
I just found the LSAT Trainer to be better since it has all the subjects in one book so it is easier to carry around, whereas PS you have to buy separately. So more money and more carrying around to do.
In the end of the day it is a personal opinion, they are both great.
In terms of how to study for the LSAT, I would start off with learning the basics by reading and doing the drills through these types of books, then proceed with doing timed practice tests and learn through experience and time pressure. In the end of the day that is what the LSAT is, so get used to the testing conditions.