In reply to control freak:
Not a expert on this, but my 2p worth.
If you want to use it for nav I don't think the cheaper GPS watches will do this. They record your postion but only the more expensive models (Garmin 310XT?) allow you to pull out a grid ref. That would put you down the cheap dedicated GPS or phone route.
As regards phones, (it's what I use):
Advantages:
GPS works well, lots of apps such as strava and sporttracker available. In terms of nav can use very simple app to get grid ref or go the whole hog with mapping from memory map or anquet, (pirated maps may be available...)
Disadvantages:
Hammers the battery, probably good for maybe 6hrs? depending on phone and app used.
Fragile in terms if weather resistance