It depends on who you ask. DJs continually wonder why brides and grooms treat the mobile DJ -- the type who lugs around his equipment to show up at big events and weddings -- as a commodity. In other words, couples price-shop ruthlessly, as if any given DJ were interchangeable with the rest.

Paul Arnett (http://www.mybigdaydj.co.uk), a Yorkshire DJ and NADJ (National Association of Disc Jockeys) member who organizes the UK's Mobile DJ Show North event (http://www.djshownorth.co.uk), puts the problem like this: "Well, your average couple spends hours deliberating over the dress. You hand-pick the caterers. You pore over flowers and sweat over the florist. You spend hours choosing just the right venue and church -- not to mention the time spent on favors.'

"But then, you go out and hire a DJ because he's ten dollars cheaper than the next one. Or he's a friend of your brother's, or he does Tuesdays at the local bar. You might never even see him work, check out his equipment, or meet with him personally to make sure he's suitable."

Most couples handle every other major item in their budget differently. You don't choose one venue over another because it costs a hundred dollars less. Few brides with a budget to work with buy their cakes from the discount grocery store, even though that cake (slathered in tubs of "BetterCream" frosting) would be much cheaper than one from the designer bakery downtown. Instead, they investigate. They take pictures. They taste-test amaretto fillings and hors d'oeuvres. And eventually, they settle on the vendor who seems poised to deliver the best experience to their guests.

-- Why Is It So Different With DJs?

Part of the answer is an image problem, says Paul. "People perceive that most mobile DJs will turn up fifteen minutes ahead of time, with a couple of speakers and some cheesy circa-1970's light screens, and play 'Agadoo' all night." (For we lucky few who haven't heard it, the 1984 song Agadoo frequently charts as "the worst song of all time.")

We all feel confident identifying an excellent meal or a sublime dessert. But few of us feel comfortable evaluating DJs in the same way. We know that a good one can "get the party started," but we're not sure how to tell a good one from a bad one.

Some people think so poorly of DJs, they prefer to eliminate them entirely, soundtracking the dance portion of the night with iPods or laptops. This isn't easy -- it requires you to rent expensive sound equipment, find someone to mind the iPod, possibly buy insurance, and somehow get around or ignore the technical issues, like the inevitable three second delay between songs you get on an iPod. And yet some people find that preferable to risking the "Agadoo" or "Chicken Dance" scenario on their Big Day.

An iPod might well be better than a bad DJ. But the DJ is a key part of your five-hour reception, and some of them are very good indeed.

-- When She Was Good, She Was Very Very Good

Perhaps it's hard for the average bride and groom to grasp the difference between a green DJ with low-end equipment, and a seasoned one who knows how to transform shy and retiring Clark Kents into dance floor superheros.

The first may be nothing more than a glorified CD changer. He may or may not have a firm grasp of the different musical needs that accompany standard reception rituals, like the cake cutting or the father/daughter dance. He may lug in his entry-level Peavy subwoofers and arrange his sound system in ways that ignore your venue's peculiarities.

The second may have emceed hundreds of weddings. Along the way, he's developed something subtle but important known as voice and personality -- not an imitation of some radio host's, but his own. He doesn't practice on your wedding; he brings his skills to it, along with a top-of-the-line sound system, which he'll arrange differently depending on factors like whether or not your venue is broken up into several chambers (the cocktail lounge and the banquet area, for example).

If he's a gearhead, he might even offer specialty lighting abilities you might not think of, such as the ability to shine gobos on the dance floor -- gobos being customized templates that display things like your wedding monogram. Some DJs even offer giant video screens and live replays of key points in the reception.

But the most important skills a good DJ will bring to your wedding is a honed personality, a formal-friendly image, and an absolute mastery of what gets crowds on their feet.

Okay, so you get it. You understand that not all DJs are alike, and that a good one brings as much your wedding as any premium florist or baker. So how do you find him?

-- Choose DJs that Take Their Job Seriously

Skip the part-timers -- they're still learning the ropes, and they'll be practicing on your wedding. Instead, look for full-timers who show their commitment to the profession by belonging to professional DJ associations such as CPDJA, ADJA, & NAME, or NADJ in the UK.

Paul adds, "Ask if they have public liability insurance (in case Grandma trips over a speaker wire) and PAT electrical test certificates (to insure their equipment is safe). This also shows they're professionals and not cutting corners."

Meet with them in person, and take a gander at their sound systems. You might not know your Geminis or Peaveys from your Mackies or QSCs, but even a casual glance should tell you whether the DJ or company invests in good equipment. In fact, most will be delighted to run you through their top-of-the-line systems if you give them the slightest excuse.

While you're there, take a look at their promotional photos and videos. Are they wearing tuxes? Do they look sharp? Does their sound stage sport garish self-promoting signs, or do they keep things discreet?

-- Turn on Your X-Ray Vision

Everyone has what it takes to pick a great DJ. You simply have to meet with them in person, and absorb what they have to offer.

Paul says, "Talk to them -- their personality should shine through. While you're there, ask them what special qualities they can bring to their wedding. Ask how they're prepared to work with you to make your day extraordinary."

The DJ should be happy to meet you, seem interested in the specifics of your venue, and ask questions. "Any DJ who seems phased or reluctant by any of this -- they're not the one. If your DJ seems bored, or gives you the sense you'll be just another date on their calendar, they're also not the one."

-- A Coda for the Couple

It's true with the cake, it's true with the steak tartar, and it's true for your DJ -- the final word is quality, not price. As Paul puts it, "When you look back on your wedding reception in years to come, do you want to remember what a fantastic time everyone had? Or do you want to say, 'Well, at least we saved some money on the DJ?'"

Good DJs see themselves as part of the larger picture. They expect to work closely with your coordinator, photographer and videographer, and to custom-fit their setup to your venue. So hire a good DJ -- one who can help you tailor the night's entertainment to your individual wedding.

"And see what they can offer to make your wedding function unique," adds Paul.