From the pics, the Zalman is lower and has less clearance, and as your mate probably found the Tuniq is touch and go to get in there.
BUt, having not handled the Zalman, it may be that it's just the way the pic looks, but it does look like it'll catch on the copper fins on the rearward side of the cpu socket, and if it doesn't actually foul them, it will leave so little clearance as to be no fun at all to install. Damn fine looking cooler though.