Whey the Sansa over the Ipod? How's the compatibility with Itunes? I use a Mac and that's where all my music is.

I'm looking to invest in a good portable setup. I need something light and compact because I want to use this mostly for working out. It needs to fit in a pocket fairly comfortably, or be able to clip onto a waistband or an arm. I've been using my old Iphone 4 as an Ipod since I've upgraded my...