For attention-seekers, the GS is better. The body is lowered, and the front end gets the biggest flared-nostril air inlets this side of a Lamborghini, along with trapezoidal exhaust outlets and optional 20-inch chrome alloy wheels.

The springs are roughly 20 percent stiffer front and rear, and the rear antiroll bar is 20 percent larger. The front brakes are powerful Brembo units with four-piston calipers and 14-inch rotors. The GS adopts the 2-liter engine from the Turbo, but the boost pressure is increased by 33 percent. That raises the horsepower to 270, from 220, and increases the torque to 295, from 260.

Just how serious is this Buick? Before the recent introduction of a 6-speed automatic, the GS came only with a 6-speed manual transmission.

The cabin of the GS, like the ones in basic Regals, is stylish and smartly appointed, despite a few bits of mismatched trim. Additions for the GS include a metal-trimmed flat-bottom steering wheel and handsome leather sport seats with body-cupping bolsters. After 20 years in which G.M. has handed out tickets to cheap seats, I’m beginning to see and feel relief in some of its newer models.

Another gain is the seven-inch navigation touch screen, a feature that will migrate to most Regals next year.

On the highway, the car feels as solid and quiet as any Audi, Volvo or Lexus. On the downside, it weighs a chubby 3,710 pounds.

The GS also erases major flaws of standard Regals: the straining 2.4-liter engine of the cheapest versions and the upsetting torque steer of the Turbo.