I've had the 72-piece set of Prismacolors for years (eight to be exact), and I had most recently acquired the full set of Polychromos. I was wondering what the hype was all about, so I went ahead and got some. To test the two different type of colored pencils, I colored a couple of pages from Johanna Basford's Lost Ocean, using Prismacolor Premiers on the left, and Polychromos on the right. I also included on the pic the pencils that I used. The pics were taken prior to using Gamsol, or a blending stump.
Here's a closer look at the fish scales colored with Prismacolors. A lot of white areas were showing through.
The Polychromos took to the paper better. I'm skipping the tortillons and Gamsol on this one.
I noticed when filling out the chart that Prismacolor had brighter hues, while the Polychromos were more subdued. Here's a link if you want to have your own color chart.
I will be using my Polychromos more, since I love the ease of blending, but I will also be supplementing it with Prismacolors, which still has the best variety when it comes to skin tones. :-)