Font-family and compatibility between Linux, Windows, MacOS X

Introduction

It's quite hard to choose a font-family that will work similarly and nicely on all OS.
Some useful links on the subject:

one of the best font-family (though somewhat too large) with good explanations is: 8 Definitive Web Font Stacks
statistics on fonts available on various OS: combined font survey results

Tests

The table below tells what font you get on various OS for a given font-family:

font-family Mandriva Linux
2009.1 - 2010.1 Ubuntu 8.04 Ubuntu 8.04
with msttcorefonts MacOS X Windows

font-family: sans-serif DejaVu Sans [#1] DejaVu Sans
[#1] DejaVu Sans
[#1] Helvetica Arial

font-family: Verdana N/A N/A Verdana
[#2] Verdana Verdana

font-family: Arial Liberation Sans
[#3] N/A Arial
[#2] Arial Arial

font-family: Helvetica Liberation Sans
[#4] Nimbus Sans L
[#5] Nimbus Sans L
[#5] Helvetica Arial (?)

font-family: Helvetica Neue N/A N/A N/A Helvetica Neue N/A

font-family: Geneva N/A N/A N/A Geneva N/A

font-family: DejaVu Sans DejaVu Sans DejaVu Sans DejaVu Sans N/A N/A

font-family: Bitstream Vera Sans Bitstream Vera Sans Bitstream Vera Sans Bitstream Vera Sans N/A N/A

(A monospace font has been added to the font-family to show the fonts not available)

font-family	Mandriva Linux 2009.1 - 2010.1	Ubuntu 8.04	Ubuntu 8.04 with msttcorefonts	MacOS X	Windows
font-family: sans-serif	DejaVu Sans [#1]	DejaVu Sans [#1]	DejaVu Sans [#1]	Helvetica	Arial
font-family: Verdana	N/A	N/A	Verdana [#2]	Verdana	Verdana
font-family: Arial	Liberation Sans [#3]	N/A	Arial [#2]	Arial	Arial
font-family: Helvetica	Liberation Sans [#4]	Nimbus Sans L [#5]	Nimbus Sans L [#5]	Helvetica	Arial (?)
font-family: Helvetica Neue	N/A	N/A	N/A	Helvetica Neue	N/A
font-family: Geneva	N/A	N/A	N/A	Geneva	N/A
font-family: DejaVu Sans	DejaVu Sans	DejaVu Sans	DejaVu Sans	N/A	N/A
font-family: Bitstream Vera Sans	Bitstream Vera Sans	Bitstream Vera Sans	Bitstream Vera Sans	N/A	N/A

Explanations

Helvetica, Arial and Liberation are mostly the same,
Helvetica/Arial and DejaVu are quite different (DejaVu being much larger),
DejaVu and "Bitstream Vera" are mostly the same,

"font-family: sans-serif" gives the wider DejaVu on Linux,
"font-family: Helvetica" gives similar results (on Ubuntu, it's somewhat different),
"font-family: Arial" gives very similar results, but is not available on Ubuntu without ttf-liberation nor msttcorefonts,

Conclusion

If you want your web site to look very similar to Arial on the various OS, use:

font-family: Arial,Helvetica,sans-serif

Notes

#1: Ubuntu and Mandriva have a specific fontconfig configuration (cf 1 and 2) (It seems Ubuntu's configuration comes from Debian, but Debian doesn't have it anymore).
Fontconfig's default configuration is to prefer Bitstream Vera since commit "Prefer Bitstream Vera to DejaVu families" in 2006.
#2: The package "msttcorefonts" installs Microsoft "Core fonts for the Web".
#3: "Liberation Sans" is very similar to Arial.
#4: Mandriva specific fontconfig configuration.
#5: This is fontconfig default configuration.

Hint: to know which font is used under Linux, use fc-match (eg: "fc-match Verdana").