After four full years on the market, you'd think someone would have come up with an entry-level luxury car to rival the current BMW 3 Series. Perhaps by now an automaker would have bribed a BMW engineer to fork over the blueprints, or maybe had its CEO take a 3 Series, hand it to his engineers and say, "Here, copy this." Indeed, the 3 Series is often imitated, but somehow it's never been duplicated. For unparalleled driving excellence, the 2010 BMW 3 Series is still where it's at.

As is typically the case, BMW has relentlessly improved this 3 Series since its debut in 2006. For '07, the 335i's twin-turbocharged inline-6 debuted, an engine that has been showered with critical praise ever since, and a sleek coupe and retractable-hardtop convertible also joined the lineup. For '09, the sedan and wagon's controversial taillight design was rectified, and a gloriously torquey and fuel-efficient turbodiesel inline-6 became available for the sedan. Heck, BMW even managed to fix iDrive last year, thanks to a proliferation of physical buttons and a much-improved menu structure. All of that partly explains why the 3 Series is still the most desirable car in its class, even at the ripe old age of five.

The other part is the inherent goodness of its chassis. Quite simply, no other entry-level luxury model can match the 3 Series' exquisite combination of athletic handling and premium ride comfort. Even the base suspension setup is more capable than most, but the Sport package really brings the 3 into focus, giving it sports-car-grade cornering capabilities without the slightest hint of impact harshness. The performance numbers are impressive in themselves, but this car transcends them -- it feels even more confident and composed than those numbers suggest.

The 2010 BMW 3 Series has long been America's best-selling luxury car, and we see no reason why it won't retain its crown. Automotive journalists and consumers agree that the 3 is the segment leader, which highlights its irresistible appeal to enthusiasts and casual drivers alike. There are worthy rivals, of course, including the powerful Infiniti G37, the striking Cadillac CTS and the Euro-chic Audi A4. But even as the twilight of this model's production run approaches, the 3 Series continues to reign supreme.

The 2010 BMW 3 Series is available in sedan, wagon, coupe and hardtop-convertible body styles. The base model for all styles is the rear-wheel-drive 328i, while the coupe, sedan and wagon also come in all-wheel-drive 328i xDrive guise. All but the wagon are available as the rear-drive 335i, while the sedan and coupe can be had in 335i xDrive form. The range-topping sedan model is the diesel-powered 335d.

Standard equipment on the 328i models includes 16-inch wheels, heated side mirrors, premium leatherette vinyl upholstery, automatic climate control and a 10-speaker CD stereo with HD radio and 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 is similarly equipped but includes xenon headlamps and a sunroof.

The Premium package adds leather upholstery (heat-reflective in the convertible), auto-dimming mirrors, Bluetooth connectivity, BMW Assist telematics and, on 328i models, a sunroof and power seats with driver memory. The Sport package specifies a firmer suspension on convertibles, sedans and wagons (the coupe already has this as standard) 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 xenon headlights and a sunroof (328i only), automatic high beams, a hard-drive-based navigation system with the 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, rear window shades, satellite radio, an iPod adapter and a Logic 7 surround-sound audio system.

The 328i models are powered by a 3.0-liter inline-6 that produces 230 horsepower and 200 pound-feet of torque. The 335i gets a 3.0-liter inline-6, this one twin-turbocharged to produce 300 hp and 300 lb-ft of torque. The 335d boasts a twin-turbocharged diesel engine rated at 265 hp and an enormous 425 lb-ft of torque. All gasoline-powered models come standard with a six-speed manual shifter, while a six-speed automatic with available paddle shifters is optional (standard on the 335d).

In performance testing, we've clocked 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 require a bit more than 5 seconds to reach 60 mph. The 335d did the sprint in 5.9 seconds.

According to the EPA, the 328i gets 17-18 mpg in the city, 25-28 mpg on the highway and 20-21 mpg combined, depending on body style and powertrain. The 335i with the automatic achieves 17 mpg city/26 mpg highway and 20 mpg combined, while the manual transmission and all-wheel drive lower those numbers slightly. The 335d is rated at an impressive 23 mpg city/36 mpg highway and 27 mpg combined.

Standard safety equipment on the 2010 BMW 3 Series includes antilock disc brakes, stability control, 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 the top rating of "Good" in its frontal-offset crash test. The 3 Series also scored a "Good" for side crash protection except for the convertible, which received the second-lowest "Marginal" score.

Driving is what the 2010 BMW 3 Series does best. The 328i's naturally aspirated inline-6 is otherworldly in its smoothness from idle to redline, and it has enough power to suit most tastes. Those in search of something more will be well-served by the twin-turbo 335i, which maintains the 328i's refinement while adding a huge wallop of torque that's always on tap. The 335d is perhaps the biggest hoot of them all, serving up face-flattening torque off the line and a uniquely muscular soundtrack while using the least fuel of the bunch.

When the going gets twisty, the 3 Series' sublime suspension, steering and brakes will provide endless entertainment. Sport package-equipped models can even keep pace with many genuine sports cars. At the same time, the 3 Series is a wonderful long-distance cruiser, boasting 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 2010 BMW 3 Series interiors will be familiar to anyone who has spent time in a BMW product. Classic analog gauges, sensible ergonomics and a restrained overall aesthetic combine to create a pleasant driving environment, though there's less visual pizzazz here than in some rivals. The base seats are comfortable and supportive, the Sport package's purpose-built seats even more so. 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. The revised iDrive electronics interface that comes with the optional navigation system is not only greatly improved over its confusing predecessor, but also one of the best interfaces of its kind.

The rear seats are adequately roomy for adults on shorter trips, but taller passengers will complain that their heads are crammed into the roof. 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 predictably shrinks considerably when the top is lowered.