I'm using the IZ3D driver at the moment Neo and they are actually quite mature, having played with 3D Vision as well, they are comparable. The are two big problems I picked up with IZ3D though:
1. I had to download the beta driver for support for DX10 and DX11. I haven't noticed any problems so I suspect it will be merged into a new release soon, making this less of a problem.
2. Finding a decent screen. A lot of 3D screens are ONLY compatible with Nvidia's 3D Vision (like your Asus screen Neo), I'm not sure of the technical reasons why. Eventually I settled on the Zalman 24" (which was very difficult to find) and the screen is quite glossy, if you don't dim the lighting it is quite reflective. 3D Vision users definitely have a better monitor selection.
So definitely, 3D Vision is a more complete solution. Easy to find good quality compatible screens, the glasses, graphics cards and drivers are all maintained by NVidia. ATI isn't left completely out in the cold though.