Different tab widths are a non-issue. Sure, the maximum character per line only works for a set tab width, but I take that “problem” over the rigidity (and unsuitability) of spaces as indentation.
It becomes issue when mixed with spaces. Say, aligning function parameters on multiple rows. If the indentation of the second row of parameters is mainly with tabs, and then adjusted to place with spaces, it's suddenly a huge issue. And that will happen.
So spaces only for me, thanks.
Tabs for indent, spaces for alignment - solves the problem unless you're trying to align across indentation levels, but you probably shouldn't be.