I vote for the Regal.
The Cadillac's have a dismal quality record, and have enough electrical gizmo's to make you cry.
The Regal has the ubiquitous 3.8 liter all iron V6, and is incredibly durable and reliable. It also gets unbelieveably good gas mileage. You are likely to get 30 mpg on the freeway.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".