Copic Ciaos come in a more limited color number (144) & they hold less ink than a Sketch marker. They are round, which means they feel more like a SU or Tombow marker in your hand. Ciaos do not have the color # on the cap. This will mean more to you once you'd start using them. Ciaos are also slightly less expensive.
Copic Sketch are oblong shaped. They come in the complete range of colors (334). They hold more ink than Ciaos, which means less refilling. I like the Sketch because better for these reasons.
If you plan on buying, consider avoiding the sets. The sets are arranged in the order the colors came out in production, not in natural blending families. Check out this link to help you decide what colors to get your feet wet:
http://ilikemarkers.blogspot.com/200...tart-with.html
I hope this helps, and I hope you love your Copics as much as the rest of us do!!