With turbo-4 engines the easiest to compare, and multi-link independent suspensions teamed with electric power steering and optional adaptive ride controls, the mass-market editions duke it out, the ATS pulling up as evenly as any sedan ever has with the Bimmer. It's the 272-horsepower ATS turbo-4 that takes on BMW's 240-hp turbo-4, with nearly identical acceleration times, and a choice of manual and automatic transmissions, as well as rear- or all-wheel drive.
Of course, there's always the nuclear option: the BMW M3 (or M4, as a coupe), with 425 hp, or Cadillac's new ATS-V sedan or coupe, with 455 hp. We'll handle that shootout on a separate line item. Yeah, we'll take one for the team.
Between the less lofty versions, which holds the real performance edge? It's really too close to call; even in straight-ahead stability and cornering transitions, Cadillac's dialed in the cornering magic that used to be the province of BMW's MacPherson struts and links. Neither car requires the expensive upgrade suspensions, though Cadillac's magnetically-controlled shocks seem to have more sublime control than BMW's adjustable setup.
With even fuel economy nearly identical, the BMW 3-Series and Cadillac ATS sedan still offer a clear choice. The BMW fans we know wouldn't consider looking elsewhere. Now that Cadillac's in the business of selling phenomenally balanced handling in a compact package, with superior looks and a tech interface second to nothing in the class, it puts that long-standing loyalty to a severe stress test. The fact that ATS sedans are widely, and heavily, discounted, makes the choice all that more difficult.
The ATS isn't a knockout blow to the Bimmer, but it's thoroughly good where other four-doors like the Lexus IS, the Infiniti Q50, and Acura TLX come up ever so slightly short. It's the most nimble, tossable Cadillac ever. And it's a more electrifying entry, since it's new, and since in a system called CUE it offers one of the most tightly integrated telematics and infotainment systems short of a Tesla Model S.
The ATS may inch ahead in the ratings when we're all done adding up the 2017 numbers, but you'll need to peruse the our full reviews in order to figure out which one suits you best—and which is the new archenemy.