I understand that you want to know which is the recommended firmware version for the Slingbox AV.
I recommend you to use the latest firmware version for the Slingbox AV (1.2.12). If you are using the SlingPlayer software version 1.5, just open the SlingPlayer software and go to the Slingbox Directory.
Once you open the Slingbox Directory and go to "Edit". Select the "Slingbox Configuration" tab and go to "Update Slingbox Firmware". This way, you should be able to get the latest firmware version for the Slingbox AV.