I don't personally know what Petruchio
intended, but in my opinion (FWIW) it should depend on how your editor saves the resulting file. If it preserves the TAB character, vote TAB. If it converts the TAB to spaces, vote the number of spaces.
I configure TextPad so that it converts new and existing tabs to 3 spaces, thus I voted 3 spaces. That way it doesn't look crappy if it's printed using some other editor than I used to create it. Unless, that is, it looked crappy to begin with or some formatting issue other than the default tab size comes into play.
A related followup poll suggestion: The one true line length. :-)