The Opel based Catera (the Caddie that zigs) will be difficult to find parts for soon.
It's smaller than the LS therefore the ride will not match the longer wheel based LS. The LS also has options for V6 or V8 power. Between the two, I'd do the Lincoln, and I'm a life-long GM guy.
The Caddie is cute, and will undoubtedly give you better mileage than the LS. The two cars are aimed at different consumer markets. Difficult to compare.