I suspect the visco clutch is better as it will always give some air motion, even if bad. The electric clutch lets the fan freewheel if it fails, unless it locks up.

The W115 220D and 240D don't have a clutch, don't know about the W123.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!