I have KDevelop set so that pressing tab indents, and yet it saves as spaces. Pressing backspace unindents, if you know what I mean; it erases four spaces at once. So saying that tabs save time is really not the best argument.
Saving as spaces is really the way to go. Spaces display the same way, no matter what the editor.
Of course, spaces give you slightly larger file sizes, but compress really well.
That's just my opinion. My official advice is to pick one, stick with it, and don't mix them.