Ford Mustang (© Sam VarnHagen/Ford Motor Co.)

Automakers are locked in a popularity contest every day. They wrangle with each other for the hearts, minds and money of car-hungry consumers, and their popularity ebbs and flows as they continually develop their vehicle lineups to better appeal to the American masses. Cars must have an ideal mix of styling, reliability, utility and value to rise to the head of their respective classes. As long as those best-sellers maintain that delicate mix, they tend to stay in the top spots for years — that is, until a new or completely overhauled model comes along to challenge their supremacy. Here, we examine 10 all-new or seriously refreshed machines destined to challenge the sales leaders for dominance in their respective classes.

Bing: Best-in-Class Vehicles

Challenger: BMW X3

Class: Premium compact crossover utility
Class leader: Audi Q5
The X3 kicked off this class when it was introduced for the 2004 model year. Sales were strong for a couple of years, but then took a nose dive because of consumer concerns over ride harshness, interior quality and back-seat room. The arrival of serious challengers from Acura, Audi, Mercedes-Benz and Volvo didn't help, either. According to data provided by Automotive News, only 6,075 X3s were sold in 2010, a quarter of what the class-leading Audi Q5 sold. However, a 2011 redesign that addressed the X3's former issues put it back in the game. The availability of a turbocharged 6-cylinder engine also gives the X3 more power than ever, making it our choice as the most engaging vehicle in this segment.

View Pictures:  2011 BMW X3

Challenger: Chevrolet Cruze

Click to enlarge pictureChevrolet Cruze Hatchback (© General Motors)

Chevrolet Cruze Hatchback

Class: Compact car
Class leader: Toyota Corolla
The compact-car market has seen a flood of new products in the past year, and just about all of them raise the quality bar for the class. The Chevrolet Cruze is a prime example. Compared with Chevy's previous compact offering, the Cobalt, the Cruze has a sportier, more refined character, much improved fuel economy and a far more upscale interior. The performance of its automatic transmission remains an issue; even so, this is General Motors' best compact car ever. Also watch out for the new Ford Focus and Hyundai Elantra.

Compare: Chevrolet Cruze vs. Toyota Corolla vs. Ford Focus

Challenger: Dodge Grand Caravan

Click to enlarge pictureDodge Grand Caravan (© Chrysler Group LLC)

Dodge Grand Caravan

Class: Minivan
Class leader: Chrysler Town & Country
While there are only five players in the minivan segment, every one underwent a redesign or update in 2010, and that is sure to affect the status quo in this segment. The 2010 leader was the Chrysler Town & Country, with around 112,000 sales. The Honda Odyssey followed closely, at 108,000, and the Dodge Grand Caravan came in third with 103,000 units sold. Sure, the Caravan and the class leading Town & Country are siblings. And yes, both received updates for 2011 that gave them nicer interiors, better handling and a more powerful and efficient engine. However, a shift in market positioning means that the Town & Country's price tag now starts at more than $30,000, while the Grand Caravan sells for less than $30K. We think this will tip the scales in favor of the more affordable Dodge.

View Slideshow:  The Mighty Minivan

Challenger: Ford Explorer

Class: Midsize crossover utility
Class leader: Ford Edge/Chevrolet Traverse
The Ford Explorer changes classes for 2011, from the midsize SUV segment to midsize crossover utility. The all-new sport-utility vehicle is better in almost every way; it handles much better, it has improved interior materials and cutting-edge tech features, and it gets much better fuel mileage. Plus, despite the changes, it maintains some impressive off-road ability, thanks to a Land Rover-derived terrain-management system. Given those strengths, the Explorer should vie with the Ford Edge and Chevy Traverse for the lead in its class.

Watch Video:  2011 Ford Explorer

Challenger: Ford Fiesta

Class: Subcompact car
Class leader: Honda Fit
The Ford Fiesta is a true upstart in this class. Depending on how you define the subcompact-car class, the Fiesta is either a shoo-in to lead the class in sales or a strong contender. Last year, the segment was led by either the Honda Fit, with 54,000 sales, or the larger Nissan Versa, with close to 100,000 sales. After the first three months of 2011, the Fiesta is selling better than the Fit, but it trails the Versa by about 10,000 units. We think all three are strong, fun-to-drive offerings in a class otherwise known for budget-minded cars that lack passion.

Bing Images: Ford Fiesta

Challenger: Ford Mustang

Class: Sports car
Class leader: Chevrolet Camaro
The Mustang had the American sports car market to itself from 2003 to 2009, leaving it to compete with the likes of the Nissan 350Z and Mazda Miata. Last year, however, the sexy new Camaro, available only in coupe form, outsold the Mustang, which is offered as both a coupe and a convertible. Given that Chevrolet is adding a convertible this year, the Camaro will likely win again, but it shouldn't. With its powerful new engines, the Mustang is simply the better car. It's considerably more fun to drive, and the new Boss 302 is the sportiest pony car ever offered.

View Slideshow:  Sports Cars: Best Bang for the Buck

Challenger: Fiat 500

Class: Microcar
Class leader: MINI Cooper
The tiny Fiat 500 faces only two competitors: the smart fortwo and the MINI Cooper hardtop. While the smart is fading fast, the MINI is tough competition. That doesn't mean the 500 can't compete, though. It possesses the same kind of Go-Kart handling that makes the MINI so fun to fling, while offering lower prices and better fuel economy. But will American buyers trust an Italian brand just coming into the market, and will the 500 catch on using the MINI's mix of cute retro looks and trendy appeal? We suspect that it will.

View Pictures:  2012 Fiat 500

Challenger: Hyundai Sonata

Class: Midsize car
Class leader: Toyota Camry
No automotive category is as competitive as the midsize-car segment, and it has been dominated by the Toyota Camry and Honda Accord for the past several years. But the Hyundai Sonata is gaining traction. While Toyota sold 327,804 Camrys in 2010, Hyundai pushed almost 200,000 Sonatas, an increase of 64 percent from 2009. The new Sonata continues as a good value, while also offering plenty of interior space, stylish good looks, a powerful turbocharged model, a trendy hybrid and a fuel-efficient base engine.

Compare: Hyundai Sonata vs. Toyota Camry vs. Honda Accord

Challenger: Jaguar XJ

Class: Full-size luxury car
Class leader: Mercedes-Benz S-Class
Although it is a long shot to supplant the heavy-hitting BMW 7-Series and Mercedes-Benz S-Class, the redesigned Jaguar XJ has already done a lot to re-establish the brand in the prestigious full-size luxury-car class. Sales are three and a half times greater than last year through the first three months of 2011, but still only about a third of the S-Class's total sales. We think the XJ will gradually gain market share in this segment, thanks to bold good looks and a sporty character matched only by the BMW. In addition to premium luxury, buyers in this class look for emotional appeal, and the XJ has both in spades.

Read:  Hot Grilles: 10 Best Front Ends in Auto Design

Challenger: Kia Sorento

Class: Compact crossover utility
Class leader: Toyota RAV4
If you classify the Kia Sorento with 5-passenger crossovers such as the Honda CR-V and Ford Escape, it won't be able to contend for the segment lead. However, if you place it with 7-passenger competitors such as the Toyota RAV4 and Hyundai Santa Fe, it stands a chance. Kia sold 108,985 Sorentos in 2010, the first time any Kia topped 100,000 sales, and 2011 is off to a good start, too. It'll be tough to catch the RAV4, but the Sorento's impressive cabin, useful space and good looks make it a worthy rival. A soon-to-be redesigned Hyundai Santa Fe, which will share its design with the Sorento, may prove an even stronger challenger for the RAV4.

Watch Video:  2011 Kia Sorento

Kirk Bell has served as the associate publisher for Consumer Guide Automotive and editor of Scale Auto Enthusiast magazine. A Midwest native, Bell brings 18 years of automotive journalism experience to MSN, and currently contributes to JDPower.com and Kelley Blue Book's kbb.com.