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Here are more distinctions, by category of programming:

ROCK AND POP
Both services devote a disproportionate number of channels to various forms of rock, and both slice the niches awfully thin (is a channel playing nothing but '80s hair bands really necessary?). Sirius (19 rock channels) dedicates some channels entirely to one artist -- there's 24/7 Rolling Stones, Elvis Presley and Jimmy Buffett, though Buffett's channel stretches to include similar artists. And Sirius has more channels devoted to soft rock, love songs and what used to be called beautiful music. Sirius's cool exclusive: Super Shuffle, which appeals to the iPod generation by switching randomly among all genres of popular music. XM's background music channel, programmed by Starbucks, features music heard in the coffee shops. Some aficionados say XM's rockers (14 channels) go deeper into the archives, playing more surprises than you'll hear on Sirius. Edge: XM .

URBAN/SOUL/HIP-HOPSirius is heavy on hip-hop, with four channels, including one that serves as a clubhouse for performers who leave no word unspoken, no accusation against their rivals unhurled. XM -- which has two channels of contemporary hip-hop and one of classic hip-hop -- does a much better job with old-school sounds, offering three channels of black hits from decades past. The legendary Washington deejay Bobby "The Mighty Burner" Bennett is the voice of XM's "Soul Street," a terrific trip back to the soul stations of the '60s and '70s. Edge: XM .

CLASSICAL
Both services have surprisingly limited choices of classical music. Though each service offers separate channels for symphonic sounds, voice and pops, chamber music gets short shrift, as do contemporary classical compositions. XM, reflecting its devotion to live broadcasts and concerts, has a more interesting selection of full-length performances, while Sirius generally offers more daring and edgy choices. Sirius carries NPR's fine classical programs, including "Performance Today" and "SymphonyCast," which are no longer heard on Washington's talk-oriented public stations. XM counters with "Exploring Music," hosted by Bill McGlaughlin (long-time host of public radio's riveting "St. Paul Sunday") and Davis's weekly focus on early music, "Millennium of Music." Edge: Sirius .

JAZZ
Both services have channels for classic jazz, fusion and contemporary sounds, and the background music known on FM as smooth jazz. XM's fusion channel sounds more like a jazz station circa 1978, while Sirius's plays more current electrified jazz. XM's straight-ahead channel is the better place to pick up on new artists, while Sirius shows greater range, from New Orleans through bebop all the way to today's players. In addition, both have channels of blues and American standards (Ella Fitzgerald, Tony Bennett, Mel Tormé). Sirius oddly lumps a channel of New Age and ambient sound (Enya, Yanni, Ottmar Liebert) into its jazz category. Edge: Sirius .

NEWS
A weak spot for both services. News is the most expensive programming to produce; as a result, neither XM nor Sirius has its own news operation.

Rather, both mainly use audio from TV. Both services have similar lineups of CNN, Fox, ABC, BBC World Service and C-SPAN. XM adds MSNBC, while Sirius carries Canadian and European radio services.

TV programming makes for awkward, sometimes infuriating radio, as anchors and reporters refer to visuals that listeners cannot see.

An exclusive contract with National Public Radio gives Sirius a big advantage; its three public radio channels offer fine news and talk shows not heard on Washington's FM public stations.

But the NPR deal prohibits use of the network's flagship shows, "All Things Considered" and "Morning Edition." XM's single-channel attempt to compete consists of Bob Edwards's excellent hour of interviews and some fine programs from non-NPR producers such as Public Radio International ("This American Life," "Sounds Eclectic.") Edge: Sirius .

DANCE/ELECTRONICA
Both have disco, chill, trance and dance hits channels. XM also has a channel for ravers, while Sirius adds nonstop breakbeats and mash-ups on its Boombox channel. XM's disco channel sticks closely to '70s tunes, both the hits and club favorites, while Sirius combines those oldies with '80s dance hits. Most of Sirius's dance channels are hosted by knowledgeable deejays; XM's are almost entirely nonstop music. Edge: XM .

COUNTRY
Today's hits, classic cuts and the real gritty stuff -- both services offer the basic flavors. Sirius's music choices are often more creative and surprising. Sirius adds Outlaw Country, where Fred Imus (Don's brother) does a weekend show for honky-tonk lovers, while XM's Willie's Place offers a Willie Nelson-branded selection of classics from the '50s and '60s. Edge: Sirius .

SPORTS
XM broadcasts every single Major League Baseball game all season long, bliss for fans who don't live in their team's home city. There's also an excellent 24/7 baseball talk station. Football isn't much of a radio sport, but Sirius broadcasts every NFL game, as well as the NBA. Both companies have a selection of college hoops and gridiron coverage, but XM has the corner on ACC, Big Ten and Pac-10 games. Both XM and Sirius carry ESPN's talk shows, and both air NHL games. XM adds talk channels from Fox Sports and the Sporting News; Sirius counters with a talk channel that's heavy on golf, wrestling, gambling and poker. Poker: not a radio sport. Edge: XM .

KIDS
Both services have Radio Disney and each has its own kids' channel. Sirius's is heavy on pop music and TV fare, such as audio from "Sesame Street" and "The Care Bears." Oriented toward the youngest set, the channel has lots of the Raffi and Barney fare that drives parents to reconsider the miracle of childbirth. XM Kids, by contrast, features Kenny Curtis, a veteran of Washington's 1990s experiment in kids' radio, the Radio Zone, on a morning show with running characters, sketches and contests; as well as radio theater, kids' concerts, science shows and a nightly lullaby hour. Edge: XM .

TALK
Sirius is trying to carve out an advantage in lifestyle talk with a Martha Stewart home channel, a health channel and stations programmed by Cosmopolitan and Maxim magazines. But the content is largely unlistenable, a nonstop parade of perkiness.

OutQ, Sirius's all-gay channel, is a great idea, but too often I heard club music rather than the talk shows promised in promotions. XM focuses more on advice, with financial experts Bruce Williams and Dave Ramsey, and all-night conspiracy mavens such as Art Bell and George Noory.

Both services feature political talkers from right and left, many of them syndicated hosts available on free radio -- Bill Bennett, the "NRA News" team, Bill Press and Stephanie Miller on Sirius; Dr. Laura, Laura Ingraham, Jerry Springer and Al Franken on XM. And both have channels of Christian talk and shows for truckers.

Since FCC regulations on obscenity don't apply, satellite has become the refuge for the raunch radio of the '90s.

Beyond round-the-clock Stern, Sirius has former Tampa bad boy Bubba the Love Sponge, and XM has added Ron and Fez, late of Washington's WJFK, to its anything-goes talk channel. Edge: XM .

COMEDY
Of all the programming satellite offers, the comedy channels are the biggest step away from traditional broadcast formats.

Both XM and Sirius have three channels of comedy routines; both have a choice of clean or uncensored stand-up.

Sirius has the channel Blue Collar Comedy (Jeff Foxworthy, Larry the Cable Guy, Kathleen Madigan) while XM devotes a channel to Canadian comedy. (A very high-concept joke? No, the channel exists because XM sells its wares in Canada, where the government insists on a certain amount of Canadian content.)

On its clean, family-oriented channel, XM relies heavily on classic bits (Bill Cosby, Rodney Dangerfield, Jonathan Winters and comics familiar to viewers of "The Ed Sullivan Show" in the 1960s), while Sirius seeks a more contemporary sound by using audio from more recent TV shows ("The Simpsons," "Monty Python's Flying Circus"). On the explicit-language channel, Sirius picks up audio from HBO's "Def Comedy Jam" shows, while XM plays more live appearances recorded at nightclubs in Washington and elsewhere. Sirius's admirable attempt to expand the form fails for the same reason all that TV news audio flops: Too often, you can't see what the joke is about. Sirius's edgier approach means that rather than sticking to stand-up, the channel also plays songs that weren't meant to be funny but are, such as Pat Boone's rendition of "Stairway to Heaven." You need to hear that once in your life. Edge: XM .

These are someone else's opinion, and means nothing, other than it gives a decent explanation of what each service offers.