DAB is great, if you listen to radio - more stations, better reception. A guy I worked with installed an aftermarket DAB set in his car, because he hated listening to Radio 5 on AM. He couldn't sing the praises of the unit highly enough.
The choice of stations is what swings it for me - stuff like 6Music and Radio7 offer a much better selection of things to listen to and some of the archive stuff (from Radio 4 and 1) that gets recycled on those stations is fantastic.
As for SD-Card or USB stick (which is it) vs iPod - meh, what's to argue? iPod is complex, easy to steal and they go wrong, whereas USB stick or SD Card is dead simple and they tend to get lost before they die.