What folder do you prefer? BaseCamp installs folders for Maps in a number of locations:
C:>Garmin>Maps
C:>ProgramData>Garmin>Maps
C:>Program Files (x86)>Garmin>Downloaded Maps
C:>Program Files (x86)>Garmin>BaseCamp>Maps
C:>Program Files (x86)>Garmin>MapInstall>Maps
The first location seems like a good choice for either 32 bit or 64 bit operating systems.
The second locations contains a mapset formatted differently than the standard .img files.
I don't understand the redundancy of the last three locations. Duplicate copies of the Global Application Base Map v2.gmap folder occur in the last two locations.
C:\Program Files (x86) is a read-only folder intended for programs. While you can save maps there, it doesn't look convenient. Multiple wold maps come with Garmin programs. BaseCamp, HomePort and MapInstall, each saves its own copy.
C:\ProgramData>Garmin>Maps goes along system conventions and seems to be a good place for data like maps. This is an alias for C:\Users\All Users\Garmin\Maps. These folders work for maps in gmap format.
If you want to save maps without admin rights, you can use local directory like C:\Users\(user-name)\AppData\Roaming\Garmin\Maps. This folder will work for maps in gmap format.
C:\Garmin is a convenient folder for any purpose.
Personally I save maps in folder F:\Garmin\(map-name). All maps in gmap format go to folder F:\Garmin\GMAP, which works, because I have created a link from C:\ProgramData>Garmin>Maps to this folder.