Well I just did a test of several uprez products and concluded that PhotoZoom was superior to my eye (so I bought it). I'll admit that the new Genuine Fractals 4.0 is much better than earlier versions.
We had a longish thread about the PhotoZoom vs. PS vs. Genuine Fractals here...
http://photoshopgurus.com/forum/view...ozoom&start=15
(It's a 2 page thread. I've linked the second page which has the specific comparison but to see the context of the sample image, look on the first page of the thread.)