The best stone for a homemade stream is local stone but be sure to source it legally and ethically from a local garden center or other suitable provider. You can choose to use one type of stone or mix different types of stone if you prefer. A good combination that replicates nature would be to have split stone along the banks and weathered, large and intact stones in the water. Boulders can be used as feature pieces. Also, try to match stones already in your garden, to help keep the look natural.