Like everything else about the A4 3.0, the V6 engine is very smooth. Press down on the throttle and power comes on linearly, evenly. It does not paste you to the back of the seat, but it delivers solid torque throughout the rev range. Variably phased intake and exhaust camshafts and variable-length intake runners optimize air/fuel delivery, boosting horsepower and maintaining 90 percent of peak torque from 2200-5200 rpm. So there's a deep well of power available whether you're winding up a country road or just cruising along. Jab the gas pedal in any situation, and the A4 responds immediately.

With the six-speed manual, the A4 3.0 is a match for BMW's 330i, long the performance benchmark in this class. The six gear ratios are nicely matched if you want to shift frequently and really work the engine. Yet the V6 is flexible enough that you can shift less frequently, allowing the engine torque pull the car along. But only rarely will you fall into the passive mode at the wheel of an A4. More often than not you'll want to stretch it. The six-speed itself is a nice gearbox, though not the easiest to coordinate with the clutch for smoothness. An A4 3.0 quattro with the six-speed manual can accelerate from 0 to 60 mph in 6.9 seconds and can turn the standing quarter-mile in 15.2 seconds. That's comparable to the performance of a BMW 330i.

If you prefer an automatic transmission, you have two options: an A4 quattro (all-wheel drive) with a more traditional five-speed Tiptronic automatic, or a front-drive A4 with Audi's Multitronic continuously variable transmission (CVT).

The CVT was designed to handle the high torque load of the 3.0-liter V6. It's lighter than conventional automatics, has fewer moving parts, and theoretically fewer things to go wrong. And, theoretically speaking, it always provides the optimum ratio, at any engine speed, any vehicle speed. In terms of real-world performance, an A4 3.0 FronTrak with the CVT accelerates as quickly as an A4 3.0 Quattro with the six-speed, according to Audi, and gets about the same mileage as an A4 with a manual transmission. The CVT takes some getting used to, however. Its internal clutch can take a moment to engage and respond. To the driver, this can feel like sloppiness in the drivetrain. Depending on circumstances, you get rolling too slowly, or with a jerk, and working the throttle can require some practice. It's really a matter of getting used to the CVT's different behavior. Audi has programmed its CVT with six pre-defined ranges that act like gears. The CVT can be managed by a Tiptronic-style sequential selector, so drivers can operate it like a conventional automatic with a sport shifter. We recommend driving the CVT before buying it. Having said all that, it works great and is one of the best CVTs available.

We can recommend the five-speed Tiptronic automatic for the A4 3.0 quattro with no caveats. Put it in Drive and leave it there. It offers responsive performance and communicates well with the V6. Fuel economy for the A4 3.0 Tiptronic (18/25 mpg EPA City/Highway) is comparable to that of the A4 3.0 six-speed manual (17/28). Enthusiast drivers can slide the Tiptronic shifter to the right and shift manually. Pull the handle back to downshift, push it forward to upshift. The automatic offers less acceleration performance when compared with either the CVT or manual gearbox (slower by a half-second in the quarter-mile). Still, the five-speed automatic with Tiptronic is a nice companion to the A4 3.0 quattro, making for a terrific car that we thoroughly enjoyed. There's plenty of punch here. We never tapped the steering wheel impatiently, waiting for the acceleration to build. We were never anxious when we pulled into an opposing lane to pass. And around town it shifted very smoothly.

We do not enjoy the Tiptronic as much with the A4 1.8T, however. The turbo and automatic do not seem to always work as a team. At low speeds around town, the turbo seems to confuse the transmission, resulting in reduced response, then a surging sensation. We found this alternating behavior annoying. In stop-and-go L.A. traffic the automatic sometimes seemed surprised when we suddenly stood on the throttle to change lanes; the car hesitated before taking off, not good when other cars are barreling up behind. At higher speeds, however, the automatic shifted very smoothly and we wondered whether we were being overly critical. Fuel economy with the 1.8T and Tiptronic suffers by 1 mpg around town, 2 mpg on the highway.

The 1.8T with front-wheel drive and the five-speed manual transmission is the best bargain in the A4 line. The turbocharged four-cylinder lacks the smooth, quiet operation of the V6, but it's strong enough to deliver good acceleration with the manual gearbox. The A4 1.8T is about 200 pounds lighter than an A4 3.0, and seems quicker to respond. It may be the spriest of the bunch.

Regardless of model, an Audi A4 offers responsive, precise handling. The steering is quick enough that a lane change requires only a small turn of the wheel, yet it isn't twitchy to the point where every slight movement on the steering wheel jerks the car left or right, requiring correction in the opposite direction. The A4 turns into corners with authority, but not abruptly. Rarely will you find yourself correcting your trajectory once you've committed to a curve. When driving an A4 Avant, you'll need to look in the rearview mirror to confirm you're at the wheel of a wagon. It's the only way to tell.

The A4 suspension features a newly developed multi-link arrangement in the rear. This sophisticated suspension keeps the rear tires in contact with the pavement, particularly on bumpy roads, and it delivers an even better balance of crisp handling and ride comfort. The optional Sport Package ($750-$900) includes stiffer shocks, springs, and anti-roll bars, plus 17-inch wheels and P235/45YR17 ultra-high performance summer tires.

The A4's ride is firm, even without the sport suspension; if you prefer soft and willowy, this is not the car for you. But we found the ride just about perfect: soft enough to soak up the bumps, never jarring, yet not so soft that the car seemed to float over the surface like a Toyota Camry. Take a curve at a brisk clip and you'll feel firmly planted to the road, without the excessive lean that takes the fun out of driving some sedans.

The high-performance Audi S4 boasts a lightweight, 4.2-liter V8 producing 340 horsepower at 7000 rpm and 302 pounds-feet of torque at 3500 rpm. The strong low-end torque of this V8 gives the S4 excellent throttle response at all engine speeds. Stand on it any time and it takes off. Audi claims 0-60 mph acceleration in just 5.3 seconds with the six-speed manual transmission. (The S4 Cabriolet is just a tick slower than the sedan, at 5.9 seconds.) A specially tuned exhaust announces the S4's added power.

The S4's optional six-speed Tiptronic transmission automatically selects from over 200 shift patterns to match any driver's particular style. Shift paddles located on the steering wheel can be used to shift gears without taking a hand off the steering wheel. Or, if you prefer, you can use the Tiptronic gate on the shifter console, as in other A4 models. The S4 works well with the manual gearbox and is amazingly tractable: You can creep along in first gear slower than walking pace without lurching or having to push in the clutch, and you can shift up very early when cruising sedately around town.

We wouldn't call it harsh, but the S4's ride is quite firm, maybe too firm for all but the most dedicated handling enthusiast. The S4 jostled us on a bumpy I-405 in Los Angeles and on rough neighborhood streets. Try to drink a cappuccino on the way to work and it'll end up sloshing on your hands. You feel and hear manhole covers. At times, the S4 feels like a car in search of a race track. Having said that, it feels very refined overall. It's very quiet with the windows up. Upgraded brakes and 18-inch wheels aid stopping and steering.

Quattro is a full-time all-wheel drive system that automatically shifts power to the tires with the best grip. If the front wheels are slipping, quattro delivers more engine power to the rear, more effectively turning that power into forward momentum. Quattro does more than improve traction on wet, slippery surfaces, however. It improves handling in all conditions, including dry pavement, because it distributes torque loads evenly among all four tires. Thus, neither the front or rear tires are too overworked to grip in a corner.

All A4 models come with an electronic stability program (ESP), a computer-managed system that gently applies the brake at any one of the four wheels to help counter skids. All told, these systems make the A4 one of the most secure handling, confidence-inspiring small sedans in production.

The Audi A4 has excellent brakes. We gave the brakes a good workout on the road up and down Vermont's Mount Equinox, where sports car clubs run organized hill climb competitions. This road is a series of tight hairpin turns connected by straightaways, and you'd better be able to count on your brakes. The A4 slowed itself with authority, and we didn't experience a hint of brake fade, even after repeated full-on stops with little recovery time in between. That's reassuring. The A4's ABS programming with Brake Assist senses panic-stop situations, and applies maximum braking even if the driver hasn't fully pressed the pedal. Quattro, ESP, and automatic brake proportioning are seamlessly integrated and usually transparent to the driver.