Another year, another round of subtle changes to make one of the most heralded automobiles ever made even better. For decades, the BMW 3 Series has been the benchmark in the entry-level luxury car market -- be it in sedan, coupe, convertible or wagon guise. Typically, this BMW has offered a magnificent blend of restrained luxury, top-notch build quality, just-right size, ample feature content and a ride/handling balance that other manufacturers have been unsuccessfully trying to copy for ages.

For the 2009 BMW 3 Series, a few changes have been made to keep its superior status intact. Some of the sedan and wagon's more questionable styling elements have been rectified. These models receive a new front fascia that's reminiscent of the sexier coupe and convertible, and their streamlined cabooses mark a return to the more attractive BMW tradition of L-shaped taillights. The coupe and convertible have been left alone this year, and that's fine with us, as the sedan and wagon were the only members of the family that needed some cosmetic surgery.

Elsewhere, the much-maligned iDrive electronics interface has been dramatically improved, with more logically arranged menus and buttons surrounding the iDrive control knob that access frequently used functions (radio, navigation, telephone). The navigation system itself is now hard-drive-based and features real-time traffic information.

Later in the year, BMW's first clean-diesel engine for the United States will debut in the 2009 335d. This twin-turbocharged six-cylinder will make prodigious power and yet manage remarkable fuel economy of 23 mpg city and 36 mpg highway, according to BMW, while meeting the latest strict emissions requirements of all 50 states.

The 2009 BMW 3 Series is poised to remain America's best-selling luxury car, and for good reason -- it's an honest-to-goodness driver's car that's nonetheless comfortable and stylish enough to appeal to a wide range of consumers. This isn't to say that there aren't other worthy contenders. The Infiniti G37 offers 335i power for 328i money, the Cadillac CTS offers an extra dollop of interior room and the latest Audi A4 offers all-weather capability in a stylish package. All are admirable alternatives; however, none is good enough to knock the 3 Series from its traditional perch.

The 2009 BMW 3 Series is available in sedan, wagon, coupe and hardtop convertible body styles. All come in base rear-wheel-drive 328i trim, while the coupe, sedan and wagon also come in all-wheel-drive 328i xDrive guise. All but the wagon are available in rear-drive 335i trim, while the sedan and coupe can be had in 335i xDrive form. Later in the model year, a diesel-powered 335d sedan will arrive.

Standard equipment on the 328i models includes 16-inch wheels, heated side mirrors, a sunroof, leatherette vinyl upholstery, automatic climate control and a 10-speaker CD stereo with an auxiliary input jack. Coupe and convertible versions come with slightly more equipment, including a sport-tuned suspension on the coupe and a power-retractable hardtop on the convertible. In addition to its more powerful engine, the 335i adds 17-inch wheels, xenon headlights and power front seats with driver memory. The 335d should be similarly equipped.

Most 3 Series cars you find on dealer lots will be equipped with the Premium Package, which adds leather upholstery (heat-reflective in the convertible), auto-dimming mirrors, Bluetooth connectivity, BMW Assist telematics and, on 328i models, power seats with driver memory. The Sport Package specifies a firmer suspension on convertibles, sedans and wagons, and all get larger wheels, sport seats and steering wheel, and special "Shadowline" exterior trim. The Climate Package adds heated front seats and steering wheel, retractable headlight washers and fold-down rear seats (though the latter are unavailable in the convertible). Many of these items can be had as stand-alone options.

Among the à la carte options are a navigation system with iDrive controller, keyless ignition/entry, active cruise control, front and rear parking assist, an active steering system (335i only), paddle shifters for the optional automatic transmission, xenon headlights (328i), rear window shades, satellite radio, HD radio, iPod adapter and a Logic 7 surround-sound audio system.

The rear-wheel-drive BMW 328i and all-wheel-drive 328i xDrive are powered by a 3.0-liter inline-6 that produces 230 horsepower and 200 pound-feet of torque. The 335i and 335i xDrive get a different 3.0-liter inline-6, this one twin-turbocharged to produce 300 hp and 300 lb-ft of torque. The 335d will be powered by a twin-turbocharged diesel engine rated at 265 hp and a pavement-rippling 425 lb-ft of torque. All gas-powered models come standard with a six-speed manual shifter, while a six-speed automatic is optional (standard on the 335d). Paddle shifters can be added to the auto.

In performance testing, we've spurred a 328i sedan with the manual transmission from zero to 60 mph in 6.4 seconds, while the heavier convertible is a few tenths of a second slower. We've tested a variety of 335i sedans and coupes, and they consistently do the sprint in just a shade over 5 seconds. The 335d did the sprint in 5.9 seconds.

Despite its potent power plants, the 3 Series remains relatively fuel-efficient. The 328i gets 17-18 mpg in the city, 25-28 mpg on the highway and 20-21 mpg combined, depending on the body style and drivetrain. The 335i with the automatic achieves 17 mpg city/26 mpg highway and 20 mpg combined. The manual transmission or all-wheel drive will lower those numbers slightly. BMW estimates fuel economy for the 335d will be an impressive 23 mpg city and 36 mpg highway.

Standard safety equipment on the 2009 BMW 3 Series includes antilock disc brakes, stability control, run-flat tires, front-seat side airbags and full-length side curtain airbags. The convertible lacks the side curtains, but the regular front side airbags extend up to head level, and there are also pop-up rollover hoops. The stability control system integrates several features designed to improve braking performance, such as periodically wiping the brake rotors dry when the windshield wipers are in use, and automatically snugging the pads to the rotors when the driver abruptly lifts off the throttle.

In government crash tests, the sedan and wagon received four out of five stars for frontal collision protection and five stars for side protection. The Insurance Institute for Highway Safety gave the 3 Series sedan, wagon and convertible the top rating of "Good" in its frontal-offset crash test. The sedan and wagon also scored a "Good" for side crash protection, but the convertible received a second-lowest "Marginal" score because of insufficient rear seat head protection and possible torso injuries for those in the front.

There's no going wrong with any of the engines available in the 2009 BMW 3 Series. The naturally aspirated base engine is a little light on low-end torque, but it moves the car smartly once underway and provides laudable fuel economy on the highway. In the BMW tradition, this inline-6 is velvety-smooth from idle to redline, yet the tailpipes emit a purposeful bark under hard acceleration. For the power-hungry, the twin-turbo 335i is a riot, providing the kind of acceleration formerly associated with the high-performance M3. Meanwhile, the late-availability 335d provides face-flattening torque off the line while using the least fuel of the bunch.

No matter which model you choose, the 3 Series' world-class suspension, steering and brakes will provide hours of entertainment on twisty two-lane byways. At the same time, the 3 Series is a wonderful long-distance cruiser, delivering both a supple ride and a hushed cabin. The 3 Series' long-running double act is truly extraordinary: It speaks the language of driving enthusiasts, yet its upscale image and comfortable interior give it unrivaled mass appeal.

The 3 Series interiors provide a restrained show of luxury. Though a tad plain, the emphasis is on driver comfort and involvement through elements such as supportive seats and clean analog gauges. Materials and build quality are exceptional; even the standard leatherette (vinyl) upholstery looks and feels better than one would expect. The convertible's available heat-reflective leather does a wonderful job of keeping occupants' posteriors cool. This year's revised iDrive electronics interface that comes with the optional navigation system is improved over its confusing predecessor, but it still complicates the stereo controls.

The standard front seats have enough firm support to ward off fatigue during a day's worth of driving, while the optional power-adjustable sport seats are sublimely comfortable. The rear seats are adequately roomy for adults on shorter trips, but taller passengers will wish for more headroom. Trunk space is average in sedans and coupes, while the wagon offers a maximum cargo capacity of 61 cubic feet. The convertible offers a reasonable cargo hold when the hardtop is up, but it predictably shrinks considerably when the top is lowered.