I’d avoid WMA and use MP3 where possible. Anything will play MP3. All hardware music players support MP3. All software music players will play MP3. At the higher bitrates common today (192kbps or 256kbps), MP3 and WMA’s audio performance is comparable.

iTunes can convert your free music downloads that are WMAs to MP3 or MP4 on import.

You can also configure Windows Media Player to import (rip) your CDs as MP3, rather than WMA.