The only season I've seen of "24" from beginning to end was the current one, where she didn't seem too bad. As for previous episodes, I only have hearsay evidence and can't honestly comment.
If I had to vote, I'd go with Adam Mitchell from the first series of "Doctor Who". He's the genius who decided to have major (and needless) brain surgery after carefully considering the matter for 10 seconds, and is still the only Companion whom the Doctor actually kicked out of the TARDIS. Utter doofus!