From what I've heard, WMA files sound fairly decent when compared head-to-head with MP3s. You might not notice any difference between WMAs and MP3s at that bit rate.

However, MP3s have a large base of applications that will work with them, and they can be played on any computer. WMA files, on the other hand, are limited to Microsoft's utilities and operating systems. For instance, if you want to edit the tag information on your WMA files, you can't use all the great mass-editing utilities like MP3 Tag Studio or Tag And Rename. And if you want to do things like cut and splice the files, you will have to convert them to a wave format and then re-encode them (resulting in quality loss) instead of using something like MP3Trim.

So even if the quality is the same to your ear, there are still advantages to MP3 over WMA.

Note that there are some great MP3 creation packages available for download. Most notably, the programs AudioGrabber and Exact Audio Copy (EAC). If you use these with the latest version of the LAME encoder (also free for download), you will get very high quality files and will also be able to use all of the other MP3-related software programs.