Running at 4k resolution with DSR should provide better image quality than running at 1080p with AA on unless those games have a supersampling option that exceeds 4x SSAA. Do note that 4k resolution is insanely demanding, and you're not likely to get great framerates if you turn DSR up that high unless you're running GTX 780s or higher in a two way SLI setup at minimum. Single GPUs aren't going to do well at 3840x2160, if you're lucky a single GTX 780Ti or 980 might squeak by with 30FPS, and even then you might have to turn some settings down to stay above the 30FPS mark.