On the plus side the Copic colored images (orange) are vibrant and have an enormous about of depth. On the minus side the Copics can cost upwards of $7 a piece and the paper you use can be quite pricey as well. You also must understand blending and shading to use them to their full potential.
On the minus side Prismacolored images with OMS lack the depth of the Copics and can look quite grainy. On the plus side the Prisma pencils are not nearly as expensive as the Copics and quite frankly just about any colored pencils, including the Dollar Store variety, will give the same results. While an understanding of blending and shading will certainly help, you can easily have quicker success with colored pencils.
Both images below were colored on Georgia-Pacific paper which is very economically priced but I don't like the Georgia-Pacific with the Copics. It is much too porous and dries too quickly to blend as well as I would like. On the other hand I absolutely loved it with the colored pencils.
So what is my personal preference?--Copics--and probably not for all the reasons you think. I do like the vivid colors of the Copics and the depth but believe it or not one of my main reasons I like using them is because I have always held my pencils too tight. As a result I have an unsightly knot on my middle finger. Coloring with the Prismacolor pencils is no different. My hand becomes easily fatigued and I just can't do as much as I would like. I have missed using my pencils and am going to make a conscience effort to use them more often. BTW I have no affiliation with either company, have not taken any classes on using either product and am not an artist by any means...I can't even draw stick people. These are just my personal opinions.
I wasn't very happy with the picture of the card I uploaded previously. One of my digital cameras is really weirding out so here it is again. I'm entering it in the Birthday Sundaes "Anything Goes" Challenge and Copic Coloring Challenge at Color Me Copic.
Below is the card I colored with the Prismacolor pencils and OMS
I'm entering it into the Bling It On Challenge "Anything Goes."