The iTunes 1080p videos are currently the highest-quality videos of the show available. They are true 1080p videos, unlike the HDTV rips which are deinterlaced 1080i videos. The iTunes videos have rich details that often get blurred out in the HDTV rips, and while the 1080p videos have slightly more compression artifacts than the 720p videos, the improvement in resolution makes up for it.
Open these two links in different tabs and rapidly switch between them for a comparison:
The colors are still less saturated, but I don't think that's a bad thing (though most people do).
The videos come with subtitles, so that'll make transcribing the episodes much easier the subtitles have been multiplexed in by fans.