I have used a Garmin during some sessions. I wear it inside my PyroPro. Based on where I am riding and wind direction I either put it on my back or chest in order to try to orient towards the best satellite reception.
I like seeing all the data at the end, in particular the max speed. I take it home and connect it to the computer as well. Interesting to see the route overlayed on a map.
I am not sure I trust the max speed though. I think the sample rate is dirrerent between units and may be adjustable as well. I would like to think my max was correct, but it is hard for me to confirm.
I have done some digging around on the web regarding the speed records. From what I understand there is one particular unit that is prefered for recording the max speeds. It may be yours!
Have fun with it, and share any more information you find.