[xorcist]

Short version: spaces doesn't break over time.

Longer version: First understand that there is no tabs vs. space. There is only tabs + spaces vs. only spaces. (Because not all indentation line up with tab spaces, and someone may wish to line up assignments, lists, etc.) Only one developer in the history of your project that uses another tab stop standard is then enough to mess up your indentation. And that's just one way to mess it up, in a sufficiently large project some creative developer will find another.

Spaces just work and ensures your guidelines are followed. The only downside is a few wasted bytes. It might have been a religious debate in a long distant past when someone actually counted bytes, but today it's mostly young developers who don't know better who engage in it (with a few exceptions). Linus uses spaces. OpenSSL changed to spaces as part of cleaning up their codebase. It's the default behaviour of GNU indent. It is a good idea.

[cortesoft]

Right, but how many spaces?

[collyw]

4