When I'm traveling overseas for business (rare these days, but I think I recall "once upon a time"...) I always use(d) public transportation. Same for US cities where it makes sense -- NYC & Washington DC. Typically if I"m travelling to another city, even with a subway or groundline system (CLE or PDX, for example), my clients are spread all over the place and there's unfortunately not a good way for me to cover it all without a rental car.

On holiday travel...I always use public transportation whenever I can!