ipod choices

i finally gave in and bought an ipod touch. something i'd been avoiding for a long time.
Now the question is what do i do with my CD's i'd like to rip? rip them in mp3 format or put them in apple's aac format?
Honestly the only way we listen to music is through the ipod or an ipod clock radio (at least for now), so I am uncertain which format is best.
i'll investigate further.
regards,
makingourway