It is a general question.

The iPod Touch is much slimmer, due to it being flash based, and the Zune being HDD.

The touch can function as a watered down PDA, while the Zune cant even achieve that.

And from what I know, the Zune doesnt have a web browser.
Making WiFi useless.

Go for the iPod, much better option, unless you have a huge media collection.

 

The iPod touch won't function as a PDA out of the box and will need to be hacked to give you any functionality like that.

 

However, due to the simplicity of "hacking" (or jailbreaking) the iPod Touch and the amount of help that one can receive from these boards, turning the iPod Touch into a "watered-down" PDA isn't a large battle. It's definitely worth buying the iPod Touch and jailbreaking it.
If you do buy the iPod Touch, I am referring you to Bowlerguy10.
He helped me jailbreak my 1.1.2 iPod Touch and if you get a 1.1.1 iPod Touch than he can help you even easier. Message me with any other questions.
I hope that helped!

 

ipod touch, very slim and has a web browser, official doenloadable apps are on the way if you dont like hacking.

zune, not really viable for mac users and non u.s. (for store anyway) and wifi is very limited so no web browsing, it is also bigger than the 160gb classic ipod.