Just as primaries and caucuses define the year’s political landscape, these three big technology trade shows compete to introduce trends that will shape 2008. Each show has its own personality and its own surprises – and its own part in influencing whether a few months from now we’re all clamoring for new iPhones, wireless HD home theaters, or the next challenger to Facebook.

Apple’s iPhone announcement at Macworld stole the buzz last January, and for the rest of the 2007. Image: Apple

New design in HP’s business displays (Photos 1-5) Flash storage and more in HP’s redesigned laptops (Photos 1/6) HP’s new Blackbird: The Lexus of PCs? (Photos 1/6)

Which show will prove most influential?

Though there’s just one company at the heart of it, don’t bet against the Macworld confab in San Francisco, where Apple (AAPL) unveils its latest strategies and dares the digital world to answer the challenge. Apple has always gotten attention – after all, super-showman CEO Steve Jobs could sell candy to Willy Wonka – but the company’s recent momentum helps, too. Apple happens to be the hottest thing in technology right now, with a lineup that includes the trendy iPhone, profit-minting iPod and resurgent Mac.

Though Apple’s iPhone announcement at last year’s Macworld was arguably the most-hyped electronics debut ever, the product itself didn’t disappoint. So everyone will be watching the stage on January 15 to see if Jobs & Co. can do it again in 2008. The thriving Mac rumor ecosystem expects thin, flash-based laptops, a major software update for the iPhone, and movie rentals on iTunes. Bottom line? If Apple has anything to say about it, 2008 will be all about feather-light wireless devices sporting powerful software and video playback.

But first, the rest of the tech titans will have their chance to steal Apple’s thunder. Next week at the mammoth Consumer Electronics Show in Las Vegas, luminaries such as Microsoft (MSFT) Chairman Bill Gates, Intel (INTC) CEO Paul Otellini, and Comcast (CMCSA) CEO Brian Roberts will meet in the desert to share their vision of the future with more than 140,000 attendees and exhibitors including Hewlett-Packard (HPQ), Research in Motion (RIMM) and Sony (SNE). A major theme this year: delivering high-definition entertainment to homes, cars and phones.

For tech journalists and industry insiders CES is half hell-hole, half wonderland, with the world’s coolest cell phones, cameras, HDTVs, game systems and in-car electronics spread over 1.8 million square feet of leg-cramping exhibit space. This is the show where many people got their first glimpses of advances like futuristic OLED displays, digital home theater and home automation systems. But it’s also a stage where tech execs make big promises that don’t amount to much.

At the other end of the spectrum is an event that draws just a few hundred people. At the end of January, some of the freshest new ideas in tech will be on display at DEMO, an invitation-only gathering outside Palm Springs. There, veteran tech analyst Chris Shipley stages the tech biz version of Survivor, where a closely guarded roster of innovative startups (and a few big companies) gets a few minutes to demonstrate a breakthrough new product or service in front of an elite audience of venture capitalists and corporate kingmakers.

Much of the DEMO fare isn’t for the mass market – you won’t see the next Nintendo Wii unveiled here. Instead, these are the technologies that Silicon Valley insiders often acquire or imitate, and incorporate into their own arsenals. (Intuit (INTU) a few weeks ago announced plans to buy former DEMO presenter Homestead Technologies for $170 million, and HP last year bought former DEMO presenter Bitfone for an undisclosed sum.)

So DEMO might not be big, but it’s hot. And if you really care about which way the tech industry is headed, it makes sense to pay attention to January’s little show, along with the San Francisco Applefest and the Las Vegas Gadgetfest.