Serif typefaces are very traditional. They are similar to one another as they each have an extra decorative element on the ends of each character ("feet"). Serif typefaces work well in print in text heavy layouts which have many body paragraphs. When used in text heavy documents, the reader will respond favorably and better retain the information.
Sans-serif typefaces are similar to one another in that they are smooth (no "feet") and work best for print titles and on screen body paragraphs. On screen design benefit from sans-serif typefaces as they appear to be "smoother" and are the preferred typeface for readability on websites.
Decorative typefaces are varied and range in readability. Some are appropriate for body paragraphs, while others should be restricted to use in logos and artistic text elements.