Dyneema/Spectra is the the way to go as long as there is a good weight on the end.
The comments about it being low stretch is correct i have seen a dyneema rope pulled to its breaking strain on a test bed and cut, it basically just fell on the floor, but the same cant be said for the covers that usually are on the outside of the line, they will recoil when broken under load, for that reason i know several operators that dont run a cover on there lines.
As for the comments on chain snapping, i dont agree if the chain is tested and inspected it won't happen on a helicopter(provided the correct size chain is being used) you will pull the helicopter in half before it would"snap".
The accident being referred to if its the same one im thinking of was a empty chain getting flicked or whipped into the blades.
I have used wire rope and chain along with synthetic and by far the easiest to use is the synthetic.
A bit thread creep i know