The holy war about spaces or tabs continues and you can see all sorts of arguments for each side raging around the internet.
I prefer spaces because it’s a consistent format that remains the same no matter what you are using. With tabs things appear differently depending on how your editor or other program is configured. Plus the worst thing is when spaces and tabs get intermixed.
Arguments for tabs such as they take up less room or it’s easier to move around are in my mind weak. In this day of terabyte disk drives, file size differences between tabs and spaces are trivial and most of your disk space is taken up by images and binary files anyway. And being able to move around and format quickly is not an issue either with modern editors.
The two editors I use most are XEmacs and Eclipse. Below I describe how to use spaces for indents for each program.
(setq-default indent-tabs-mode nil) ; Use spaces for indents except ; in buffers that already have ; their own local values for the ; variable.