My opinion, which is based largely on second hand info. Creative makes the better overall hardware, but their drivers tend to be garbage, which can often hamper the experience. Turtle Beach cards may not be quite as good hardware wise, but the drivers are generally higher quality.

That being said, I would DEFINITELY go with a system that connects directly to the sound card if we're talking about some kind of surround sound signal being transmitted. Those can take up a lot of bandwidth, and so I'd personally rather not take the chance it gets backed up somewhere on the USB bus.

And there's a post by some guy over in the Computer Help forum who has an issue with a USB sound card you might be interested in reading. But the long and short of it is, is that the USB bus is really a pretty poor choice for a sound card if you do much more than listen to MP3s with it.