The Color Antialiasing (Blur) slider is used only by the Best Renderer, and determines the softness of the antialiasing effect. Larger values represent more blurring. Antialiasing is an edge-blurring effect which makes rendered images appear smoother even when their pixol resolutions are low.
The Edge Antialiasing slider is used only by the Best Renderer, and determines how abrupt an edge or corner must be before it is rendered using antialiasing. If this value is 0, only sharp edges are antialiased; if 100, all edges are antialiased.
The Sample Size slider is used only by the Best Renderer, and determines how much of the surrounding area to consider when antialiasing an edge. Values can be from 1 to 8; larger values provide more accurate results but increase rendering time.
The Super Sample slider is used only by the Best Renderer. To antialias the image, ZBrush can calculate the antialiasing values for the entire image more than once, and average the results to arrive at the optimum antialiasing effect. This slider determines how many times to calculate the entire image, and its values can go from 1 (default) to 4. Higher values produce better results, but drastically increase rendering time.