The simple answer is that the heavier aircraft will (probably) have a lesser glide endurance and hence a greater rate of descent.
The rather more complicated answer is it also depends on the speed chosen. Best glide endurance, which means lowest rate of descent, is achieved by flying at Vmp. Vmp is proportional to the square root of weight, so Vmp for the heavier aircraft will be greater than that for the lighter aircraft. But both aircraft are flying at the same speed so one will be closer to its Vmp than the other.
If the speed chosen is at or slightly more than Vmp for the lighter aircraft, then that will be the one closest to its Vmp. This will tend to give the lighter aircraft a reduced rate of descent compared to that of the heavier aircraft. If the speed chosen is at or slightly less than Vmp for the heavier aircraft, this effect will be reversed, with the heavy aircraft having the advantage.
But at the end of the day the actual rates of descent wil depend upon the combined effects of the different weights and the speed chosen.
If this is a JAR exam question they are probably looking for the heavier aircraft having the greatest rate of descent. The examiners' argument will probably be something along the lines of "jet aircraft usually descend at or close to Vmd in order to get maximum range. So neither aircraft will be very close to their respective Vmp. So the weight difference will be the dominant factor, giving the heavier aircraft the greatest rate of descent."