Above is a photo of the results of using each of the tools mentioned above to cut out a curved leaf shape. The far left was the needle tool. In my experience the needle tool is the least effective is cutting and leaves a very jagged edge compared to my Ultra Clay Pick and the QuikArt Stylus. It may be hard to tell in this picture but the edge it the most jagged.
The piece in the middle was cut with the Ultra Clay Pick. I still love this tool as it is sturdy and I am used to handling it. I gives a cleaner edge to the needle tool.
The piece on the far right was cut with the QuikArt Stylus. It seemed to produce the cleanest cut. I think this would be especially useful for intricate stencils.
Overall, when testing it numerous times I didn't find a large difference in the way the Ultra Clay Pick and the QuikArt Stylus cut the edges. I am used the the feel of the Ultra Clay Pick in my hands and the QuikArt Stylus was a little different to get used to. Its tip is fine and I am a little nervous it may get bent or broken if if it the cover is not put back on it (which knowing me may actually happen in a rush).
Given the price point, I think the QuikArt Stylus is worth a buying, but I am still quite fond of my Ultra Clay Pick.
For those who are new, the other essential cutting tool is of course a craft knife. Remember to keep your craft knife blades sharp as the dull blades leave to pool cuts.
Also a note about the pieces above, I did not finish them because I wanted you to see a fresh cut. But after you cut a piece remember to run your finger around the edge to soften the imperfections before the piece dries.
Another side note, it that I used reclaimed clay for this test which can lead to more tears when cutting the clay. For the smoothest edge use fresh clay.