one argument for spaces > tabs is that with tabs you cannot see if you have (mistakenly) added spaces to indent a particular line (without :set list which can be annoying to some). If someone else opens the file and their tabstop setting was set to a different number than you, they'll see different indentation on those lines. If everyone uses spaces, everyone will always see the same thing.

I think tabs settings as something that should be agreed on by a team or project lead - too easy to screw things up. Same with line ending settings in version control if you're working with a mixed OS team.