I much prefer serifs, particularly in the context of code and the like, wherein the ability to quickly and easily discern the difference between the numeral one (1), the lowercase L (l), and the pipe (|) is of particular importance. In most prose text, the pipe character isn't even present, and there is almost always sufficient context to quickly discern a numeral from a letter, but in code, these concerns are EXTREMELY relevant.
Also, for what it's worth, more serif fonts than sans-serif fonts contain a numeral 0 which is easy to discern from a capital letter O. That, and any font I use for code has got to be monospaced, which is a limitation that yields a higher portion of serif fonts, as well.
Of course, the need to display code well covers almost every general purpose text application I use, since, being a programmer, almost any general purpose text application is likely to end up containing code (email, IM, text editing, terminal consoles, etc).
Not an editor command: Wq