Dave Bassett without a doubt. I can't even buy into the "seemed a good move at the time" as I never had us down as a basic long ball crazy gang thug of a team. I'm sorry but GT was far more astute than that and Bassett was a staggeringly poor substitute.
I think if you are going along the lines of a 'logical' appointment, Aidy would have been one of the stranger ones seeming he was an unknown, being brought in to save the club from relegation, after letting go an experienced manager. I still remember the day he was appointed - I was working at the club at the time. The chairman hadn't told any of the staff in case of a leak before the press conference, even though Sky still got a name before it was announced (the leaks were always from the training ground), so we all searched for Aidy's name. It was a time where everything seemed to be West Brom-related somehow.. and starting to call ourselves West Watford Albion! We thought we were doomed... but fortunately it turned out pretty well, and has started a trend of giving up-and-comers a chance!