Neither of us are very good at keeping secrets, so this would be difficult to figure out. If you asked someone, it would depend on who you asked based on whether they would say me or my sister. I was always and still am terrible at keeping secrets.
I always hope that no one tells me a secret because I am not good at keeping secrets. Most of the time, someone tells me something first before I can tell them not to tell me. Therefore, I would probably say that I am bad at keeping secrets. However, I have learned over time to try to watch what I say before I say it so that I don’t reveal a secret.