A few years ago, I was hiking in the Wind River Mtns. in Wyoming, and had made arrangements to meet R. J. Secor, who is the author of the main guidebook to California's Sierra peaks and passes. We knew generally where we were going to meet, but not specifically. So when I set up a camp in that general area, I went to a point that I knew he would have to pass, and left a note for him with the long/lat GPS coordinates of my camp. Because that was the way the GPS was set up out of the box. He found me just fine, but then I had to listen to a lecture about how he had to change his GPS from UTM to long/lat. The bottom line is, either way works, and can be changed at will. But if you don't want to listen to a lecture, use UTM.