The GTX650Ti is the stronger card, by a readily visible margin.
In my personal experience, Asus makes great motherboards, but questionable video cards; I had 2/4 die within hours or days of first use. I have not bought any Zotac boards. The last video card I bought was an eVGA GTX650Ti: http://www.newegg.com/Product/Product.aspx?Item=N82E16814130839
(my review is up).