If you have multiple versions of a software package installed, Shotgun Desktop will use the latest version as the default. However, it is possible to set a different default version.
To do this you can create two
Software entities on your Shotgun site.
On one of them fill in the
Versions field with the version you want to be default, and tick the
Group Default checkbox. Then on the other fill in all the other versions, you want to be available.
This should then mean that Shotgun Desktop will use the Group Default version over the others if you don’t select a version from the drop-down.
You could even have different default versions depending on the project.