I think I would prefer a role-play / what-if scenario for the reason that I simply don't care about revisiting certain types of work experiences. As a result I am likely to not remember details and even more likely to be unenthusiastic in the retelling. Interviewers should also consider that human memory is fundamentally malleable so any recollection will be at least a partial fabrication.
In role-play you can more easily lie about what they would do - in fact they can't help it because you know what you want to do, even though in the heat of the moment you will do something else. Thus your role-play is not very useful.
Research says that it is fairly easy to tell if someone is fabricating their situation (I've never caught someone, but I've only interviewed a couple people so my sample size is not significant). Thus I as an interviewer know you are telling me how you react to a real situation when under stress.
You have been in many situations over your life. Don't bring up ones you don't want to talk about.
Role-play is useful in that the candidate is telling you how they would act in a situation, which is how they think people should behave professionally. If they are making that up, then they would likely fabricate past situations as well.
I don't agree that it is easy to tell when someone is fabricating, if that someone is a proficient liar then it will be impossible, and that is the exact type of person you want to exclude from further consideration.
