I always use the MB brand coolant just because it's not that expensive. It's about $19 a gallon at my local dealer, so I basically do it for peace-of-mind. Since MB engines contain aluminum parts it's important to use a coolant that is compatible with such parts to prevent corrosion.

It's also important that the ph stays within spec because if the coolant gets too acidic it will cause the plastic radiator components to become brittle. The plastic neck that the upper radiator hose connects to is often the part that breaks, and that will leave you stranded.

I'm sure there are other coolants that work fine in MB engines, but since it's only flushed every three years the few extra dollars for the MB coolant is negligible.