"Paper" seems like the obvious answer but now we know that paper takes a lot of resources to produce. So, the real answer continues to be: NEITHER. The solution is to bring reusable bags when you shop and not just at the grocery store. For a great explanation of paper vs plastic, check out this link.
If you are interested in using reusable bags in your marketing campaigns and holiday events, let us know. We have many choices in various materials: recycled non woven, organic cotton, jute, denier, neoprene and canvas. There are sizes and styles for every budget.