Determine if you're going to use multiple music playing devices that support different audio formats. MP3 will likely play on all of them, whereas there is a chance WMA will not. Almost every audio device supports MP3 files. MP3 is the default or standard file format for lossy audio files. MP3 players and music cellphones might support WMA, m4a, or another type of audio format, but they will almost always play MP3. Additionally, WMA supports Digital Rights Management (DRM), which may prevent you from copying the music files to another device or computer. However, you can disable DRM when ripping your own music to WMA. MP3 does not support DRM, so you will never encounter problems transferring MP3 files to different devices due to the file type.
Determine if file size is an issue. WMA files tend to have better sound quality than MP3s when recorded at the same bitrate. WMA files take up less space than MP3 files for identical sound quality, but you may not be able to hear the difference between the two depending on your sensitivity and the particular recording.
Decide whether you want sound quality that is identical to that of the CDs you are ripping. WMA supports loss-less recording, but MP3 does not. Loss-less recording reduces the size of the CD Audio files with no loss to sound quality.
Determine whether you will be listening to audio that uses more than two channels of audio. MP3 is limited to two channels when recording, but WMA supports more. CD Audio has two-channels of audio while the DVD Audio format has five.