Hi Toes,
Your question covers a very wide range of devices. To keep it simple, I use a small Garmin 62 with OzTopo 3 map loaded. It is a handheld device that mounts to the handlebars as well as a car bracket. It is good for all kinds of activities such as bushwalking, motorbikes, cars etc but the screen is small.
My view is that the best device currently out there for both motorbikes and cars (including all roads, on and off road) would be the Garmin Zumo 660 with OzTopo 3 map loaded.
Hope this helps.
Cheers, TT