[RHSeeger]

The basic idea is that you use tabs to align "blocks" (ie, multiple lines at the same indent level), and then spaces from there to align line "elements")

Aligning lines in the same block

    ____var a; // indented with a tab
    ____var b; // indented with a tab

Aligning elements of a line with the previous line

    ____var a, // indented with a tab
    ____----b, // indented with a tab, then aligned using spaces

The idea being that tabs are used where it makes sense that you could change them for preference and not have things look wonky... and then spaces are used in situations where a specific number of characters is necessary.

Another alternative is elastic tabs, where tabs are used for both of those, but are converted to an indentation/alignment number of characters semantically. I like the idea, but I've yet to see a good implementation.

Personally I'm a fan of all spaces, but that's mostly because every company I've worked at has used that.