18: Buick Century
The Buick Century for the late 1990s was based on the W-Platform that almost every other GM sedan rode on. Its problem was that the car was lacking in a lot of areas which made it difficult to market under the Buick name. The Century was just about the most barebones sedan that you could get. Also, the styling was as bland to match (via The Truth About Cars).
For consumers, the Century was a confusing proposition because almost the entire car was a Buick Regal clone. The only difference in the sheet metal was that the Regal had a sportier nose. Otherwise, the two cars were identical. GM took the whole badge engineering thing to a whole new level in the 1990s and it didn’t bode well with consumers.