[yOkO]

aiff, means:audio interchange file format, an audio file format from apple computers,
while wav, is microsoft audio file format, it depends what you are using it for,(there are other options, sdii, mp3, quik time,etc.)
if you are, say, to make the music or efects for an animation that's gonna be worked in a
pc windows computer, you should bounce it in wav format,(or for sharing it with pc user for any matters)
if your burning to hear it in your cd player any of both will work, you should also choose stereo interleaved.
the itunes can do the job, although i prefer roxio toast, (there are others, you should check the one that better fit your needs).