As part of my coloring art class, I've been learning more about colored pencils. The first and most important lesson I learned is that not every pencil with color inside is a colored pencil. A true colored pencil has a binder that holds the pigment. The binder is either wax-based or oil-based. This article does an excellent job of explaining the pros and cons of each. I also learned that the type of pigment, as well as the binder-to-pigment ratio, affects the pencil's quality.
I have a lot of colored pencils. Most came to me as samples or gifts. Except for a few sets I've kept intact (like the World Colors set by Faber-Castell), I've just tossed all the pencils into a single container. It hadn't occurred to me that mixing brands (and thus, binder types and pigment ratios) could matter. I didn't know if the colored pencils I had were wax- or oil-based. All I knew is that my favorite colored pencils, the ones I reached for most often, were the Eagle Prismacolors I had as a kid that are now stubs despite my attempts to use them only on the most special projects.
Here's my first page of swatches, where I started with what I was guessing were the higher-quality colored pencils. Other than my 8 remaining stubby Eagle Prismacolors, I only have 1-3 of each of the others since they were all samples.