I'm currently editing/revising/flensing a story I'd put away for a year, getting it ready to send out, and I find myself doing this quite a bit. It occurs to me that it may not be a sign to stop editing, but rather a sign that both A and B should be discarded. If one is significantly better than the other, then that one should sing, and the writer should have no compulsion to change it. If the writer isn't satisfied with either alternative, maybe that's because both are bad.
Might both be equally good instead? I don't think this is usually the case. Because then the writer would be happy with either, and wouldn't have the compulsion to switch back and forth.