Regos are better. Way back in the dark days of the 70's I had many aircraft in a holding pattern. The only mistakes were made by BA12, PA812 and QFA 12, all of who managed to respond to the others' instructions.
Moving forward many years, there were fixed conditions agreed to by the airlines when Flight number callsigns (FNCs) were introduced; most of these have been ignored. The God of marketing and forward publishing of schedules takes precedence over safety.
However, there are some advantages of FNCs; they can avoid the trauma that aircraft changes can cause in an automated system (eg BAM viceBAB vice BAA taxies for KII....)