both are excellent devices, but deciding which is better is all about personal preference. the iPod is much easier to use due to superior design and software, but the iriver has more features. you must ask yourself two questions:
1) do i have a lot of LPs and cassettes that i would like to be converted to MP3?
2) do i need an FM tuner?

if the answeres to both questions are no then get the ipod.

about the formats, the iriver supports: MP3, OGG, WAV, WMA
the ipod supports: MP3, AAC, AA (audible), Apple Lossless, AIFF, WAV