If you need to line things up (like code that bleeds onto another line), tab it in to the same level, then use spaces.
That is fine in theory, but in practice it's very difficult to maintain. It's easy for you, or somebody else on the team, to mix up the tabs or spaces accidentally. Being whitespace, you won't notice. Using spaces is just much easier, especially with a mediocre or better editor that can expand them automatically for you. There's never guess work. It just works.
There's absolutely no practical difference for me. I hit the tab key (or >>) to indent, the shift-tab combo (or <<) to un-indent, and there's no visible difference. As for the actual indentation step size, you can pretty easily write a program (or editor extension or whatever) to automatically convert between them if you care, but 4-spaces should be a happy medium for everybody.