Please rest assured that Nvidia's TRSS-AA(TRansparency SuperSampling) is regarded as equivalent to ATI's QAAA (Quality Adaptive Anti-Aliasing). In Catalyst control center (current 9.1 drivers), ATI offers two choices for AAA: Performance and Quality.
From a while ago, roughly around the time that the 8800GTX was first released (with 150.xx forceware drivers), Nvidia improved its transparency multisampling quality so that it more closely matched ATI's performance AAA, which was far superior in comparison. Originally, Nvidia's multisampling only reduced some of the alpha texture crawling, with little to no improvement with image quality along the edges--actually worsening it in some cases. Now, Nvidia's TRMS-AA is much closer to ATI's Perf-AAA.
However, most of us with capable video cards would just rather go for TRSS-AA or Quality AAA. It is widely accepted as a rule of the thumb that the image quality of either method is overall equal, give or take a few textures and edges on different objects such as tree leaves and fence wires.
By the way, I have read countless articles on the image quality comparisons, and currently own two gaming rigs with high-end GPU's from both ATI and Nvidia. HardOCP has recently done yet another extensive research into the image quality comparisons between the two alpha-AA methods.