[Justin@Athens]

I would use the ZF Lifeguard5 fluid as referenced above. TE-ML11 is the official document from ZF (the makers of your transmission) and it specifies this as the correct fluid.

The benefit of using a synthetic is life expectancy of the fluid in my opinion-- theoretically it should last longer before needing replacement. Its friction properties should remain more constant throughout its recommended usage interval, vs a conventional ATF which may begin to become less effective and change the engagement point of the clutch packs in the transmission as the fluid is broken down due to heat and moisture. This is just my opinion however.