fontsromansans-seriftypography
This is not a technical question. However as the FAQs say this place is about
people who love to create well-structured and beautifully typeset documents
I take my shot.
I am often confused when which font family is more appropriate. Most people would suggest: "take what you like the most". But there are typographicaly reasons and I don't want to pick a font familty randomly.
I am looking for some good paper reasoning about the choice of font family, no luck so far. Are there good sources?
From page 5 of the siunitx manual:
By default, all text is typeset in the current upright, serif math font. This can be changed by setting the appropriate options:
\sisetup{detect-all}will use the current font for typesetting.
Thus, just replace the options detect-family and detect-weight in the preamble's \sisetup{...} instruction with detect-all, and your students will be all set.
Incidentally, if you run \addto\extrasngerman{\sisetup{locale=DE}} after loading the babel package with the option ngerman, you don't have to specify the options output-decimal-marker={\text{,}} exponent-product = \cdot, and number-unit-separator=\text{\,} explicitly while loading the siunitx package.
\documentclass{scrartcl}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\usepackage[ngerman]{babel}
\addto\extrasngerman{\sisetup{locale=DE}}
\usepackage{siunitx}
\sisetup{detect-all} % note: just one option still needs to be specified
\begin{document}
\sffamily
\SI{1.23}{\%}
1,23\,\%
\end{document}
Here's a non-exhaustive list of possibilities for "nice" font families -- which I take to mean that they provide both text and math fonts -- for use with pdflatex.
Computer Modern -- the default font family for TeX and LaTeX, i.e., the font family that's used if no other font family is loaded.
The following image represents the output of the MWE listed at the end of this posting using the Computer Modern fonts. (All subsequent images use the same MWE but load one or more additional font-related packages.)
lmodern -- Latin Modern. Very much like Computer Modern, but with many more glyphs, e.g., for characters with accents, cedillas, ogoneks, etc. Very useful if the language you write your documents in isn't English (which has, of course, very little need for these additional glyphs).
If the following image strikes you as near-identical to the one above, that's of course no accident, given the close dependence of the Latin Modern fonts on the Computer modern fonts. (Hint: When comparing the two images, look closely at the word "Let" that starts the theorem's statements. In this word, the space between the "e" and the t" is ever so slightly wider for CM than it is for LM. I was able to detect this difference only by switching back and forth rapidly between the two images. To detect any more-significant differences between the two fonts, it's probably necessary to display various accented characters.)
pxfonts font package. Comparing the screenshots below and above, you should notice the larger summation and integral symbols generated by the newpxmath package.
kpfonts and mathpazo packages, some important differences are immediately visible when looking at the integral and sum symbols and lowercase Greek letters such as \gamma.
Times Roman font. Times Roman (and its close cousin, Times New Roman) must surely among the world's most ubiquitous fonts. Whether that's an advantage (or not...) will depend importantly on your sense of aesthetics.
mathptmx package is passable, but if you really want good-looking mathematics in Times Roman, consider purchasing the MathTime Pro 2 package. This commercial package, which provides only math-mode fonts, provides optically scaled small glyphs for use in first- and second-level sub- and superscripts, good-looking large operator symbols (sums, integrals, ...), as well as many other goodies. Notice, in particular, the shapes of the integral and summation symbols in the following screenshot.
mathptmx package shown above, and not particularly similar to that of the mtpro2, txfonts or newtxmath fonts (see below). The integral symbol provided by the stix package quite slanted, as well as quite tall.
mathptmx and mtpro2 packages (or, for that matter, the Computer/Latin Modern font families) and is, instead, quite similar to the shape provided by the kpfonts package.
txfonts package has been revised and improved considerably. The new version, by Michael Sharpe, is called newtx. It's a package with two sub-packages -- newtxtext and newtxmath. The newtxtext package loads clones of Helvetica and of a monospaced font to provide reasonably well matched sans-serif and "typewriter" fonts.
newtxmath package, be sure to load the newtxmath package with the libertine option; doing so will set up a special set of math-mode fonts that is meant to harmonize well with the Libertine text fonts.
newtxmath package with the option libertine; this is not surprising, given that the same person (the incomparable Michael Sharpe) produced both the newtxmath and the libertinust1math package (as well as many other font packages!).
As I noted at the very beginning of this answer, this list is by no means intended to be exhaustive. Nevertheless, I hope it'll give you a good start if you need to choose a set of fonts.
There are, of course, many other font packages, most of which provide "only" text-mode fonts. Among these are the "TeX-Gyre" font families Termes (a Times Roman clone), Pagella (a Palatino clone), and Schola (a Century Schoolbook clone); one would load the packages tgtermes, tgpagella, and tgschola, respectively, to access these fonts. However, as these are text fonts, you still need to choose a suitable math font.
Here's the code that generated the images showing the residue theorem. Be sure to un-comment the appropriate font-related \usepackage statements.
\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage{ntheorem}
\newtheorem{theorem}{Theorem}
\usepackage{amsmath}
\DeclareMathOperator{\Res}{Res}
%% Choose one of the following (if not choosing the
%% default, viz., Computer Modern, font family):
%\usepackage{lmodern}
%%
%\usepackage{mathpazo}
%\usepackage[theoremfont]{newpxmath} \usepackage{newpxmath}
%\usepackage{kpfonts}
%%
%\usepackage{mathptmx}
%\usepackage{times,mtpro2}
\usepackage{stix}
%\usepackage{txfonts}
%\usepackage{newtxtext,newtxmath}
%%
%\usepackage{libertine} \usepackage[libertine]{newtxmath}
\usepackage{libertine,libertinust1math} % added 2019/11/28
%%
%\usepackage{newpxtext} \usepackage[euler-digits]{eulervm}
\begin{document}\pagestyle{empty}
\begin{theorem}[Residue Theorem]
Let $f$ be analytic in the region $G$ except for the isolated
singularities $a_1,a_2,\dots,a_m$. If $\gamma$ is a closed
rectifiable curve in $G$ which does not pass through any of the
points $a_k$ and if $\gamma\approx 0$ in $G$, then
\[
\frac{1}{2\pi i}\int_\gamma\! f = \sum_{k=1}^m
n(\gamma;a_k)\Res(f;a_k)\,.
\]
\end{theorem}
\end{document}
Addendum, 2012/06/15 -- A personal note: the upvotes on this answer earned me, earlier today, my 100th "badge" from TeX.SE. What a great site! You, fellow users, readers, and contributors to TeX.SE, are the one that make it great! Many thanks to all of you.
Best Answer
a good and detailed answer can be found also here - although it's talking about web design, I think these are good guide lines also for printed documents: http://webdesign.about.com/od/fonts/a/aa080204.htm