Personally, I prefer dual synch cords.
Seems like just one less thing to have to get pointed in the right direction...
However, the new Ikelite rig, with the slaves on fixed posts, below the first arm joint, is really good.
The advantages of using optical slaves are: 1 less hole/connector in housing, to set up. You can remove the strobe/arm/slave from the housing, and hold it by hand, to get greater range of lighting angles.