An animated GIF can only contain 256 colors, which will mean that it may not fully represent the original video. The first solution is to set the quality parameter to 100, this will produce the highest quality animated GIF's possible within the limited time available to create the capture. This will cause the time it takes to create the animated GIF will increase however, the file size will stay the same as there can't be more than 256 colors in a GIF.
Another possibility is to increase the frames per second, by increasing the number of frames per second many imperfections in individual frames are no longer noticeable to the human eye.