Properly maintained, rod is not more subject to fatigue.. it stretches much less than wire, has slightly less windage and cannot develop 'jaggers'.
However unlike wire, which starts to break down in visible ways long before it loses critical strength, rod can appear healthy until it decides to suddenly part. For distant cruising and easier repair, wire would win out.
We've had both, did in fact have a couple of occasions where the rod failed suddenly, a quick tack saved the rig. One failure was traced to improper maintenance the other to bad fabrication (the rod had been welded into the turnbuckle end).
We currently have wire rigging, with a dyneema ('rope') backstay. We did change out the standing rigging just for the peace of mind.
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)
1984 Fast/Nicholson 345 "FastForward"