@SarahGen-- I think they both work well for anxiety attacks, but they have different half-lives and may have different side effects. For some people, clonazepam works better and for others, alprazolam. Discuss your symptoms with your doctor and have him or her direct you to a drug. If one doesn't work, you can always ask about switching.
I have been prescribed both Xanax (alprazolam) and clonazepam in the past. I personally prefer clonazepam because it gives me less side effects than alprazolam. I also feel like alprazolam is more addictive because of its short half-life. I have to take more every ten hours for relief, whereas with clonazepam, I only need one tablet every twenty-four hours.
But if you only need temporary relief and if you don't have anxiety issues every day, alprazolam might work great for you. Like I said, ask your doctor.