There is no ideal, just which ever one you like. Optical is electrically isolated, so less likely to cause hum or ground loops, but those issues would be rare.
Try both, I suspect you can even try both at the same time.
Remember, Analog Out will use the DAC in the Bluesound which I think is an ESS Sabre DAC.
Optical will use the DAC inside your amp or whatever external DAC you connect it to. So, you are really weighing one DAC against the Other.
Steve/bluewizard