I like both of them.
I can use the Prismacolors on inkjet printed images and on images stamped with VersaFine. I like using them with images that were colored with Prismacolor pencils. However, I must keep the window open while using them because their solvent scent is rather intense. Plus, they seem to dry out quickly and the caps fall off too easily.
I just received my first batch of Copics and really like them. I find it easier to blend with them, though I'm just at the beginning of that particular learning curve. I also really like the colorless blender much better. I found the Prismacolor one didn't do jack.
Their odor also doesn't give me headaches.
I don't like that I really can't color inkjet printed images or use my beloved VersaFine with them.