The beta drivers are the latest ones, always. Beta drivers can indicate that they're not quite ready yet, there may be some additional changes for the final release of the driver, or it simply hasn't passed Microsoft's testing yet, and so they have to classify it as a beta.
For stability, go for the normal, release ones.
For performance, the beta drivers are generally best. But if you're into the sort of thing and have the time of day to do so, you can always test both the drivers and see which one works best for you.
Always read the release notes as well, if the release notes for the beta don't specify anything that would help or increase your performance, there's no point installing them.