Fonts - making choices

There are two types of 'font-family' names

<family-name>

The name of a font family of choice. In the first paragraph, "Arial Black", "Comic Sans MS", and "Impact" are font families. Font family names containing whitespace should be quoted. If quoting is omitted, any whitespace characters before and after the font name are ignored and any sequence of whitespace characters inside the font name is converted to a single space.

<generic-family>

The following generic families are defined: 'serif', 'sans-serif', 'cursive', 'fantasy', and 'monospace'.

serif (e.g., Times - font-family serif)

Glyphs of serif fonts, as the term is used in CSS, have finishing strokes, flared or tapering ends, or have actual serifed endings (including slab serifs). Serif fonts are typically proportionately-spaced. They often display a greater variation between thick and thin strokes than fonts from the 'sans-serif' generic font family. Examples of fonts that fit this description include the Latin fonts - "Times New Roman", "Bodoni", "Garamond",, "Minion Web", "ITC Stone Serif", "MS Georgia", "Bitstream Cyberbit".

sans-serif (e.g., Arial or Helvetica - font-family sans-serif)

Glyphs in sans-serif fonts, as the term is used in CSS, have stroke endings that are plain -- without any flaring, cross stroke, or other ornamentation. Sans-serif fonts are typically proportionately-spaced. They often have little variation between thick and thin strokes, compared to fonts from the 'serif' family. Examples of fonts that fit this description include the Latin fonts MS Trebuchet, ITC Avant Garde Gothic, MS Arial, MS Verdana, Univers, Futura, ITC Stone Sans, Gill Sans, Akzidenz Grotesk, Helvetica

cursive (e.g., Viner Hand ITC - font-family cursive)

Glyphs in cursive fonts, as the term is used in CSS, generally have either joining strokes or other cursive characteristics beyond those of italic typefaces. The glyphs are partially or completely connected, and the result looks more like handwritten pen or brush writing than printed letterwork. Fonts for some scripts, such as Arabic, are almost always cursive. Examples of fonts that fit this description include the Latin fonts Caflisch Script, Adobe Poetica, Sanvito, Ex Ponto, Snell Roundhand, Zapf-Chancery

fantasy (e.g., Matisse ITC - font-family fantasy)

Fantasy fonts, as used in CSS, are primarily decorative while still containing representations of characters (as opposed to Pi or Picture fonts, which do not represent characters). Examples include the Latin fonts Alpha Geometrique, Critter, Cottonwood, FB Reactor, Studz

monospace (e.g., Courier - font-family monospace))

The sole criterion of a monospace font is that all glyphs have the same fixed width. (This can make some scripts, such as Arabic, look most peculiar.) The effect is similar to a manual typewriter, and is often used to set samples of computer code. Examples of fonts which fit this description include the Latin fonts Courier, MS Courier New, Prestige, Everson Mono

Shorthands

Some of the properties in the guide are designated as shorthands. This means that they set the values for all the properties indicated, and as such, will override inherited values even if the inherited value is not specifically overridden. If one or more of the values for a shorthand is not specifically stated, it is set to the initial value for that property.
For example, font: 16px sans-serif is equivalent to:

font-size-adjust: none;
font-stretch: normal;
font-weight: normal;
font-style: normal;
font-variant: normal;
font-size: 16px;
line-height: normal;
font-family: sans-serif

because all unset values are reset to their initial values.

My 51 fonts

[Font family names are like strings, except one may drop the quotes around them]
The W3C standard instructs: Font family names containing whitespace should be quoted.

The 51 fonts on my 1997 machine are not the same as the fonts friends enjoy.
<SPAN STYLE="font-family: 'Abadi MT Condensed';">Abadi MT Condensed</SPAN>,
If the text does not appear changed, it seems that name is not on your computer/browser.

Abadi MT Condensed
Abadi MT Condensed, Abadi MT Condensed Extra Bold, Abadi MT Condensed Light,
Arial, Arial Black, Arial MT Condensed Light, Arial Narrow, Arial Rounded MT Bold , Baskerville Old Face , Beesknees ITC , Book Antiqua, Bookman Old Style, Braggadocio, Britannic Bold, Calisto MT , Century Gothic, Comic Sans MS, Copperplate Gothic Bold, Copperplate Gothic Light, Courier, Courier New, Curlz MT, Desdemona, Engravers MT, Eurostile, Felix Titling, Fixedsys, Flexure, French Script MT, Garamond, Goudy Old Style, Goudy Stout, Haettenschweiler, Harrington, Impact, Imprint MT Shadow, Lucida Sans Unicode, Maiandra GD, Matisse ITC, Mead Bold, Mercurius Script MT Bold, Modern No 20, MS Serif, News Gothic MT, OCR A Extended , Rockwell, Rockwell Condensed , Rockwell Extra Bold , Small Fonts, Stencil, System, Tahoma, Times New Roman, Tempus Sans ITC, Terminal, Verdana, Viner Hand ITC, Westminster,

This list shows that different fonts have their own size, weight and width attributes.
Keep common font size differences
As a result, I recommend that you only set font size to a different value on CODE, BIG, SMALL, PRE, TT, KBD, SAMP, SUB, SUP, H1, H2, H3, H4, H5 or H6, as these are the elements that are generally given differently sized text.

On these elements, you should always set font-size, since there are great differences in size between different browsers. Therefore you may like to ensure that everyone has a consistent view of your site by setting font-size on all of these elements.

Thus:
CODE, KBD, TT, SAMP, PRE {font: .9em monospace}
BIG {font-size: 1.15em}
SMALL, SUB, SUP {font-size: .85em}
H1 {font: 2.01em sans-serif}
H2 {font: 1.75em sans-serif}
H3 {font: 1.52em sans-serif}
H4 {font: 1.32em sans-serif}
H5 {font: 1.15em sans-serif}
H6 {font: 1em sans-serif}

These represent my recommended font size for each element; however, clearly personal taste varies, and therefore these are in no way fixed values.