Utawarerumono looks excellent at 720p. While I don't think it will look better at 1080p (it is not that detailed), I would get the 1080p-rip if I have a true HDTV (1920x1080). It will retain the maximum edge sharpness because there is no need to scale up.
(The Blu-ray rip is 1280x720, which means it is 720p, not 1080p.)
720p vs 1080p
The 720p images are upscaled to 1080p (via the browser). You'll be hardpressed to tell which is which.
At this point, I'm not convinced that TV anime needs 1080p. They don't seem to have the details to warrant the high resolution.
