Knowing what I do about your likely pace, I would vote for the garmin. As to the discrepancy at the start, the garmin often announces that it has acquired satellites, but seems to still be in the process of sorting it out. If you get it fired up 5 min or so before you head out the start is usually smoother and more accurate. It does often fail to match up with a mapped road. I ascribe that mostly to the vagaries of the map.
Concur on pace. I was not hustling. Also the MDC map of the Red Loop says its 3 1/2 miles, and that's what I expected.
Agree with Charlie. There is a 5k race course there that goes mostly around your route. The garmin is more likely.
Also note that for long hikes smoothing is better than one second recording because it uses less memory(?)/battery(?) (lasts longer).
The gps accuracy tends to be better when the device isn’t buried in a pocket. Not sure about the ability to have an iPhone on the outside but the watch should be easily worn on a wrist. Some have found placing the gps on a hat works best, but that’s a bit extreme.
See our trace from this morning around the paved circuit of the old 5k course until we got stopped and had to use the gravel trail. 3.5 miles.
A good point about memory/battery, one which I find often repeated on internet discussions I have come across.
My interest in comparing the Garmin and the iPhone is to learn more about the technology, the structures of GPS files, alternatives for accuracy when mapping, and software design opportunities.
Without question, when enjoying an orienteering event, I will keep things simple, leave the phone behind, wear the Garmin and deal just with the easy to hit Start and Lap buttons.