Depending on who caught you, neither experience would be better than the other. That being said, however, being caught in AB diapers would probably go over the worst. Their bulk and crinkliness combined with those cute prints would catch anybody off guard. I personally have never been caught in one, but If I were, I would have a very hard time explaining it away without making reference to being an AB.
Medical diapers on the other hand, are often more understated in terms of appearance, also, it's in their name, "medical", you could easily explain a medical diaper away as a tool for coping with some sort of bladder or bowel issue.
So yeah, I think being caught in an AB diaper would be worse.