Well I have a Zalman 22" and also an ASUS 23" monitor. The ASUS is 120Hz, 3D Vision. I really don't know which one is better. Both are good monitors. Personally I think I'd prefer the ASUS, mainly because I can freely move my head around. The Zalman (and other passive monitors) require that you sit in a specific position to see the effect. So that is a little annoying. And the active monitors seem to "pop" a bit more, I think because of the better resolution. However the Zalman is still good. The passive glasses give a much brighter image, and more comfortable because there is no flicker. And the 3D effect seems more real almost (probably because of better colors). So they both have pros and cons. I do like that the Zalman is supported by all kinds of stuff, including YouTube3D and all that. So I don't know, its your call.
You can see some more comments I made here:viewtopic.php?p=63506#p63506