There's not really a choice on whether it's HD or SD, all videos are downloaded as 720p. The choice given is for the bitrate of the video. There are two options 1GB per hour or 620MB per hours. The smaller file uses a lower bitrate which results in more artifacts during high motion scenes. If you're just downloading slow, talking head, type shows then the lower bitrate one should be OK but for faster paced stuff your probably going to want to use the 1GB option.
Developer for VideoReDo