If you've spent more than a few tracks worth of time playing with Pandora, you know that you can't access every song or even every artist you may be into. You can find plenty of music by the Pixies, for example, but another favorite from my college days, Liz Phair, is nowhere to be found on the service.

Raditaz launched earlier this month with promises 14 million licensed tracks, compared to the "more than 900,000" currently offered by Pandora. But guess what?

Still no Liz Phair. And now, seemingly, no Pixies either.

I spent the weekend playing with Raditaz and comparing it to Pandora, which I have been a fan of for close to a year. Neither service compares to the ease of hearing what you want, when you want in a way that Spotify does. But Pandora and Raditaz are both easily accessible on the Web and on mobile phones (Spotify requires the download of a desktop app), and both Pandora and Raditaz promise to help you discover new music based on your preferences and how you rate the songs you listen to.

Update: Raditaz spokesman Tom Brophy emailed to say that the lack of Pixies tunes was because of a "snafu" with Warner Music and that it should be resolved in about a week. And the service does, in fact, have those Liz Phair songs I can't get on Pandora.

"I actually will admit that you made some fair points," Brophy said in an email. "We are in the process of significantly upgrading the platform, and in particular, the algorithm that powers Raditaz stations. Our upgrade should be completed in approximately 30 days. We are also doing some work on better integrating Likes and Dislikes."

Why Pandora Is Better

In my tests, Raditaz loaded slower than Pandora.

Overall, in fact, the Raditaz interface was rather ugly and not nearly as intuitive as Pandora. Like the music I listened to, of course, the latter is a matter of personal opinion. But Pandora does have some objective pluses, including lyrics for many of the songs, as well as artist bios.

Beyond that, I felt that Pandora did a better job of finding music I like based on my rankings. When I gave a "thumbs down" on Raditaz for a Cake song, Raditaz immediately loaded another Cake song. Substitutions for artists not on the service was also weak: I was given Sheryl Crow and Kate Bush when I set up a station based on Liz Phair. At least Pandora gives me slightly better substitutes, including Lily Allen and the Cowboy Junkies as options similar to Liz Phair.

I may be imagining this, but I also felt that, overtime, Pandora is much quicker about learning what I like and don't like and turning me on to new artists. After spending several hours listening to Raditaz, I can't say I've found any new music that I like: that just doesn't happen when I spend the same amount of time listening to Pandora.

Why Raditaz Is Better

Beyond its promise of more songs, Raditaz also promises no audio ads (both sites have ads on their Web interface; Pandora also plays an audio ad every few songs).

Raditaz also geo-locates listeners to create "most popular" by location lists - something I frankly could live without. So far, the geo-location seems more about targeting ads than it is about improving listener experience.

And perhaps its biggest sell is that, unlike Pandora, you can skip through as many tracks as you want. Pandora, because of its licensing agreements, only lets you skip through so many songs in any given listening session.

Then again, unlimited skips is something I really needed to make it through my test of Raditaz since it missed so frequently in trying to match me up with music I actually wanted to listen to.