I think there are a number of different reasons why people consider certain types of aircraft as being bad, aircraft that were easily shot down, aircraft that were of a bad design, aircraft that were designed to fulfil a flawed requirement and aircraft that had become obsolete.
Badly designed aircraft are the worst in my book because they will always be completely useless, obsolete aircraft may have been the best in the world when they first came out and along with aircraft that were easily shot down or built to a flawed requirement they could be used for other purposes.
Out of the three choices I don't think any were bad designs, but I pick the Devastator as it was the least successful in my view.
Badly designed aircraft are the worst in my book because they will always be completely useless, obsolete aircraft may have been the best in the world when they first came out and along with aircraft that were easily shot down or built to a flawed requirement they could be used for other purposes.
Out of the three choices I don't think any were bad designs, but I pick the Devastator as it was the least successful in my view.