Unless you have a compelling reason to use a monospaced font, like emulating the ugly text seen on a computer screen, you should always use a proportional font. Font sizes Fonts are usually measured in units called points. This system causes some fonts to appear larger than others even though they are the same point size. Typically, 12-point type is used for body text. You can use smaller fonts sporadically, but you should generally spare your readers the eyestrain caused by reading fonts much smaller than 10- point.
Text becomes virtually unreadable at six points or smaller.
Likewise, you shouldn't annoy your reader with long blocks of large text. Random Fonts Random fonts, a term coined by Erik van Blokland and Just van Rossum, are a special class of font in which a character will appear differently each time it is printed or displayed. Intelligent Fonts Intelligent fonts are those which alter their appearance depending on their linguistic context. Computerized typography allows the introduction of aeolotropic fonts, which change their physical properties when their position changes. Thus a character's appearance may be controlled by applying phonetic or grammatic rules.