Bottom right corner for me. I've always found it easy to glance at, while not distracting me the rest of the time and the only view it blocks is downwards over the wing there, so not really needed.
I usually have a good idea, except the detailed location in town at the end of the journey and I often deviate from where it wants me to go - sometimes even at the end if I can see another way onscreen.
On the other hand I sometimes have it on for journeys that I know well, because it can warn me of traffic hold-ups and it acts as the hands-free set for my phone.
My Garmin does fall off from time to time, but with the deep dash of a Zafira and the suckers holding the microphone wire still attached, it only drops an inch and just sits there. However, I really need to clean the corner of the screen better and the sucker is getting rather old (it is a 10 year old Nuvi 610).
I'm actually going to have to change it soon, last year the map updates became too large for even just the UK and Ireland to fit - although it may be possible to use the SD card to expand the memory.
SteveW