Let the hive mind of Engadget get that for you.
"I own an iPhone 3G and I'm looking for a decent speaker / alarm clock for it. I am going to listen music in a mid-sized room, so I want nice quality speakers with solid bass. I also want to use it as an alarm clock, so it would be great if there is such a feature. The price can be low-mid to mid-high range. I was looking at the Klipsch iGroove SXT; it's powerful, slick and the reviews are good, but it doesn't have an alarm clock feature. It's no deal breaker if I can set it up from the iPhone, but I'm not sure. Thanks!"
iPod Nano / Creative Zen:
Size: 69,8x52,3x6.5mm / 55x83x12 (ZEN's twice the thickness, and is about 1/3 larger, but has a much larger screen)
Memory: 4, 8GB / 4, 8, 16, soon 32GB
Screen: 2" / 2.5", 16m colours (2" is virtually useless for video, 2.5" is fine, and Creative's screens are exsquisite)
Battery life: 24h audio, 5h video / 25h audio, 5h video (with a screen that much bigger, that's _good_)
Audio formats: AAC, Protected AAC, MP3, Audible 2, 3, and 4, Apple Lossless, AIFF, WAV / MP3, WMA, non-protected AAC, WAV and Audible 2,3 and 4
Video Formats: H.264, MPEG4 / MJPEG, WMV9, MPEG1 and 2, MPEG4-SP, DivX 4, 5, XviD
If you add the notoriously bad audio quality of iPods and the notoriously good audio quality of Creative's Zen line, it's a pretty clear win.