I generally use leaves on potatoes which like an acid soil. I should probably figure mulch the crop before potatoes in my rotation to get any benefit of lowered pH. Straw is a byproduct of grain harvest and not easily available in our area. I sometimes use black plastic mulch for heat loving crops like eggplant, peppers, melons and tomatoes. It adds no nutrients to the soil and is a petroleum product which are two reason not to use it. I make an environmental exception when I use plastic.
Newspapers are more environmentally sound than plastic.
It is a fine way to recycle them. They have very little nutrient value to add to the soil and some people are concerned with the ink. It would be wonderful if all newspapers were printed on recycled paper and if the ink were soy ink. Newspapers are acceptable in the Maine Organic Farmers and Gardeners Assn. I can't remember if I ever used newspapers as mulch.