[jibsen]

Most importantly, whatever the language or codebase you are working in/on mandates.

I write a lot of C, and given the choice, I tend to prefer tabs for indentation and spaces for alignment. I use a tab-width of 8, so the code will look fine for anyone using a lower tab-width.

Converting from tabs to spaces is a simple search-and-replace, whereas the other way is more work (there was an article here recently about algorithms to guess indentation width).