I have been using a 30g Zune for the last couple of months. I just bought an 80g ipod. There are some significant advantages to each, that the other doesn't have.
Zune:
Much bigger screen (if you're going to play a lot of videos, this is a deal maker. Get the Zune.)
Wireless synchronizing
I never used the wireless sharing aspect, nor the FM radio, but those are two more things exclusive to Zune
iPod:
The controls are simply much better.
Accessories. This is bigger than you might think. For every accessory for the Zune, there are 50 for the iPod. Your choices are much greater, and cheaper, for any accessories.
To me, it's a close call. I bought the Zune on sale (refurb) for $90. If you could get it at that price, it's a no brainer. But I prefer the iPod for the two reasons above, and at the same price, IMO the iPod is the way to go - unless you really planning on watching a lot of video. In that case, you might go with the iPod touch anyway. The Touch wasn't for me because I my main goal was to have my massive music collection available and portable, and 8 or 16 gig wasn't going to do it.