One is deadly in failure and one isn't.
Not
exactly true. It all depends on
when the line fails.
For rockcrawling, I've seen synthetic fail a couple of times....but only once do I know if it causing a multiple, end over end roll to the bottom of a canyon from a very precarious position. The occupants of the buggy were injured, one had to be medivac'd out by helicopter IIRC.
The problems with synth over wire include using it as a 'suck down' winch to load the suspension.....the top layers will work their way down into the drum and birdnest the spool making spooling out a PITA and necessitating frequent re-spooling to get it straightened out for actual winching.
The bigger problem, IME, is its abrasion resistance. Yes, they have sleeves on the last several feet of the rope that you can use to protect it....problem I've seen is the rope is touching rock in more that one spot as you're winching and it snaps. I guess the solution is to buy additional pieces of the protection sleeve, but I've yet to see anyone actually do that.
To be honest, synth is good kit. It's stronger than steel in comparable thicknesses (depending on brand) and it's SOOO much lighter. However, for me personally, I prefer the wire rope. The longevity, abrasion/heat/UV resistance and cost make it a more attractive option for me personally. But to each his own.