This is an age-old argument that will never be resolved, but here's where I'm aggregating information on the topic for reference. Personally, I've always preferred hard tabs, that are set to either 3 or 4 spaces of width (many early editors I worked with defaulted to 3, but I preferred 4, if only because it's an even number). Most developers I meet, however, seem to HATE hard tabs, and tab width varies by convention among the numerous programming languages out there (Python is 4 spaces but Mako is 2?).
I begin my journey with Wikipedia, as always, and proceed from there.
Wikipedia - Programming Style#Indentation
http://en.wikipedia.org/wiki/Programming_style#Indentation
Wikipedia - Tab key
http://en.wikipedia.org/wiki/Tab_key
Tabs versus Spaces: An Eternal Holy War
http://www.jwz.org/doc/tabs-vs-spaces.html
Why I prefer no tabs in source code
http://adamspiers.org/computing/why_no_tabs.html
Why I love having tabs in source code
http://derkarl.org/why_to_tabs.html
MythTV says "The one hard and fast rule of Myth development: don't use tab characters." Tabs should be set to 4 spaces.
http://www.mythtv.org/wiki/Coding_Standards
WordPress coding standards specifically say "Use real tabs and not spaces, as this allows the most flexibility across clients." This is pretty much how I feel about it, especially this part: "Rule of thumb: tabs should be used at the beginning of the line and spaces should be used mid-line." They don't specify the width of tabs.
http://codex.wordpress.org/WordPress_Coding_Standards
However, the Apache Project says the opposite: "4 space indent. NO tabs. Period." On the other hand, they also stipulate that JavaScript opening curly braces should always begin on a new line. They must not be up on their Crocker.
http://portals.apache.org/development/code-standards.html
Interesting argument here: "1 Tab = 1 Byte. 4 Spaces = 4 Bytes."
http://discuss.fogcreek.com/joelonsoftware/default.asp?cmd=show&ixPost=3978
Here's my preference:
Use tabs only for indentation of blocks (tabs at the beginning of the line, spaces within the line).
Set tabs to be four spaces wide.
Use hard tabs that insert a tab character instead of multiple spaces.
Reasons:
As long as everyone has set their editors to preserve tab characters when opening documents (which should always be the case), the spacing will always be consistent across editors whether or not they choose to display tabs as 2 spaces wide, 3 spaces wide, 4 spaces wide, 8 spaces or whatever. The tabs will appear to be different widths across editors, but they will always be the same relative to each other.
This, of course, is also the case with spaces, and spaces have the advantage that a space is always the same width no matter what editor you're using, but invariably you run across situations where people accidentally deleted a space, or added one, so where you have 5 indentations in an environment where spaces are used, and the width of a indented tab stop is say, 4 spaces, you have 19 spaces instead of 20, and this is a pain to fix.
I want to jump through the indentations using the left/right arrow keys, but instead I find myself going one space at a time - annoying!
Tabs take less space.
