I mash in a cooler. To account for the loss of temp. because of a reletively cool cooler, preheat you mash cooler. I start the initial water a few degrees hot(about 5), pour my water into the cooler and shut the lid for 5 minutes prior to adding the grain. I'll then check the temp. it normally has droped five degrees and the cooler is up to temp. After that the cooler is preheated and will not drop more than a degree or two an hour. If your grain is room temp your strike water should be in the 170-175 range for a normal size batch. It will immediately go into the 150s when you add the grain. From that point you can add boiling water, cold water, or just stir well to modify the temp to the exact degree during the first few minute as you are saturating the grain bed (although you should not be too far off). So to answer your question, I add grain to the water. If you are not a cooler masher then I assume it does not matter too much.