It depeneds
Sound Quality= iMod > Zune 2 > iPod > Zen (all better than average)
How reliable/well built= iMod > Zune 2 > iPod > Zen (very poor)
Screen: Zen ( very good) > Zune 2 > iPod and iMod
Ease of use, functionality (imo) Zen (disagree with Apok, find it very easy to use) > Zune 2 > iPod + iMod
Not to sure on battery, the iMod is thirsty though.
I really would NOT reccomend the Creative Zen, or any Creative Sound cards as there reliability is terrible, frequent lock ups, computer wont recognize them, totally die etc