Copper here. I've never installed any large Al wire, but I've taken plenty out that would still be in use if it were copper. The NEC allows it, and it is written in the specs on some jobs. So therefore, someone will always use it.
Ask a lineman which is better. You don't see PoCo's out there stringing up copper MV and HV lines. The answer is that there are applications for both. Big, if I was in your shoes, I would look at it on a "case by case" basis.
Cu later,
Doc
