Tabs really only works easily when everyone's using the same editor settings. Otherwise, it quickly devolves into a mess.

Spaces really only works easily when everyone uses an editor that can convert presses of the tab key into some number of space characters.

The only solution that works easily in all cases is to flatly refuse to collaborate with others.

> Spaces really only works easily when everyone uses an editor that can convert presses of the tab key into some number of space characters.

Could you show me an editor that doesn't do that?

I just finished three years in a job in which I worked on a GUI containing an editor that does not do that.

I'd personally say 4 spaces on even indentation levels and tabs everywhere else.