I was still adding to my post #3 when I saw post #4 so it might be worth another read
There are pros and cons to OSM, pros are more up to date, more detailed and free, cons are the maps tend to be bigger (more detailed), this can sometimes crash GPS units, I have both Garmin maps and OSM maps on my units (they can exist side by side), I tend to use Garmin maps for driving to a destination as they are more reliable, I use OSM when I get to the destination as they show much more detail