Welcome to GJ, skh! There are probably more opinions to your question than there are members here. And I believe there are several threads already on this topic.
First, check the 'Search' feature in the black band at the top of this page. If you don't find anything that answers your question perfectly, then post the question under 'General Garage Discussion' and you will get many answers, some of which are helpful. This thread is more for introductions and doesn't get much foot traffic.
But please do not mention 'PVC' and 'air lines' in the same thread...
As for me, I will probably go like 3/4 or 1" lines to use them for some storage of the compressed air. And black vs galv... whichever is on sale at the time. They both should work about the same.
Good Luck and Welcome again!