I'm not talking about programming font, but for font(s) for design docs, documentation, web pages, etc.
Which one wins? Times New Roman 10pt, Arial 12pt, Verdana? Does anybody have science to back their opinion?
Most municipal/government organizations use Helvetica for public signs. It is also the most widely used font in advertising. If you are at all interested in typography I very much recommend Typography Workbook: A Real-World Guide to Using Type in Graphic Design by Timothy Samara .
For print, there's so many fonts. Helvetica is the most popular and one of the more "readable". However a variety of fonts all look really nice, serifs like Bodoni to sans-serifs like Letter Gothic, Futura, or Knockout.
On the screen, fonts with wider letters and a more generous x-height tend to be easier to read. That said, fonts like Verdana are a bit too plain at larger sizes. Helvetica is a great workhorse font for print, as are Frutiger and Univers, but Windows machines most likely lack this font. At small sizes Arial is a poor substitute for Helvetica because of its seemingly narrow letters (due to pixel restrictions), but kern (letter-spacing) it a little tighter at 16px+ sizes and make it bold, and it suddenly will become very usable, especially for building a strong grid. A font with some quirks is always nice and interesting visually, like Trebuchet MS (see the header of this page). These fonts too, have a low x-height and aren't as visually 'clean' to read through.
The solution is Lucida Grande: functional and quirky enough to look "different." Its Windows counterpart is Lucida Sans and Lucida Sans Unicode, which should be on more Windows machines anyway, more than the new Microsoft fonts like Calibri, etc. You'll find that both Windows fonts are needed, Sans looks right with bold text and some sizes, and Unicode looks right with the rest. I think this is the font to use mainly to make long body text look less boring, since it gets tricky to use at various sizes and weights.
Also, from a developer's standpoint, there is nothing as beautiful and functional as a nice monospace font. So it really depends on your content, since if you have a load of copy to fit into a defined area you're better off with Arial. But sites these days see so much Arial being used. Lucida Grande / Sans Unicode is hands down a better font. It's always a good idea to have a pair of complementary fonts, so use a serif font like Georgia (the web's workhorse) and play around with the upper-casing and letter-spacing too.
Here are the top ten fonts used my newspapers around the US.
2. Franklin Gothic
7. Century Old Style
9. Bureau Grotesque