Having suffered through two of them, my vote would be the Vega. Honorable mention would go to the Chevy Citation, Chevette, and the forgetable Beretta.
The AMC cars were ugly, but not infamous for bad engineering. The Pacer was ugly enough to make a freight train take a dirt road, and the Gremlin had to be the worst name ever given to a car, even worse than the Dodge Demon.
Now there was a car that had some serious quality issues.
