Edited by Robert Edmonds The full edition with pictures can be viewed by clicking on the link above.
Choice of GPS depends on why you want a GPS
If you want it as a portable atlas which displays where you are then you need a good display unit and must be prepared to pay for the maps to be installed in the unit. I would suggest that learning to read a map is a cheaper alternative. Probably a useful start is to try a car GPS and see how useful they are on roads, and the problems you encounter.
You can do all sorts of things back at home base with downloaded tracks of when, where, and how you went, heart rate, cycling cadence…. However only map makers and athletes in training really need this analysis.
Personally I would hire or borrow a unit and find out if it is really what you want. Most of us on the Victorian orienteering scene are using Garmin Forerunners for our athletic training and there are numerous models of these.