There is no one "right" font in advertising materials, though there are some general guidelines for making media more readable.
Print: Use ornamental fonts for big titles only, sans serif fonts for headers and captions, and serif fonts for large bodies of text (ie a paragraph description). Serif fonts are good for this purpose because the little "tails," or serifs on the letters better help our eyes to connect the word. Body text shouldn't be smaller than 10pt to be sure it is readable.
Screen: Sans serif fonts. Try to stick with fonts that are system fonts, such as Arial, for online newsletters/websites/etc. This makes it easier to ensure that the font won't be distorted or misinterpreted across different systems. Text read on screen should generally be larger (min 12-16px).
Some robust serif fonts: Garamond, Times, Sabon, Minion, Baskerville
Some good sans serif fonts: Arial, Helvetica, Futura, Gill Sans, Myriad, Univers, Franklin Gothic
The above are basic fonts, but well developed and versatile. There are many more.