Chrome plated bolts are more susceptible to embrittlement and brittle fracture than chrome carriers. DPMS chrome bolts immediately come to mind as having problems like this. I don't recall ever hearing of problems with chrome carriers breaking, but I have heard of chrome peeling off of the carriers. I have never seen any of these problems in person, just heard/read about these problems here.
I'll add that I have run DPMS chrome carriers with park'd bolts and haven't had a problem. I also run the JP stainless without problems also.
The simplest and most reliable carrier is probably the plain Jane carrier that comes in every AR. The "enhanced" RRA carrier is a slight improvement in my book, especially if run with a smooth topped hammer (not notched - neutered M16).
A heavier, M16 bolt carrier may enhance operation due to its extra mass, but then you walk that grey line of legality that raises so much stink around here.