Water Conservation - Which is better?

With energy costs rising around the nation, each property owner should find ways to conserve where he can. Water conservation for landscape maintenance is one place to look to cut costs. By applying the appropriate ground covering mulch, water evaporation can be reduced saving water consumption. Some say that wood barks are the ideal mulching materials. Others believe decorative rock is more sustainable and does as good a job.

Which do you think is more environmentally friendly and which would conserve our resources better?