PR helped me a lot -- started out at 33 on first diag, scored 41 on actual exam.
I think the greatest value came from the 6 or so real-length, proctored MCAT exams they made you sit through (the last 2 were actual MCATs that PR purchased for their students -- btw, Kaplan does not purchase real MCATs and only gives out their self-written exams). After having done it so many times, the actual exam day is less harrowing. You could just buy the real MCATs yourself, but only if you have the self-discipline to sit there under real test conditions every 2 weeks.
The teaching was ok, but it's variable. PR approached me to teach so I learned how they recruit, and I think the quality of your teachers is very much luck-of-the-draw.
The books were pretty decent, but I would recommend the Examkrackers series much more highly -- they are more concise, more readable, and really emphasize the highlights of what you need to know. I actually only studied my Examkrackers books, then attended PR lectures and exams.
As far as Kaplan goes... I never took a course, but my friend did and complained it had nothing in common with her real MCAT exam. I also know someone else who was scoring in the high 30s/low 40s on the Kaplan diags, then got a 27 on his actual MCAT.