The three connections that you are looking at are all different and each one is a little bit better.
Video is made up of 5 signals: Red, Green, Blue, Horizontal Sync, and Vertical Sync
To carry this signal, you need five cables which are shortened in length to: RGBHV (red, green, blue, horizontal, vertical)
To properly carry these five signals you need 5, 75 ohm cables.
This can get quite pricey, very quickly, but moreso, is not required for the video signal.
That is, the fully value of RGBHV on separate cables is really utilized by high resolution computer displays running at resolutions near 1600x1200 and beyond.
HDTV is currently limited at a 1920x1080 interlaced signal or a 1280x720 progressive signal. So, it doesn't require, or utilize the full bandwidth available to it over 5 separate cables. So, while RGBHV is potentially better at the lowest level, the reality is, that you just end up with a lot of wasted space. It's like offerring someone a full size SUV when all they need to do is drive themselves to work. A lot goes to waste.
Now, RGBS, is a 4 wire connection. The 2 syncs, horizontal and vertical, are combined onto a single cable. You lose a little bit of overhead, but for HDTV, still have a lot of room left. Basically, this is still more than you need.
Component video, is always 3 wire. It adds the sync on top of the other colors and was determined to be the least number of wires necessary to carry HDTV signals at 1080i and 720p. Not sure if 1080p will have enough room to be carried over 3 wires, so that may be forced to RGBHV or digital over DVI/HDMI.
So, which one will provide the best image for you? All of them! You have the available space with component video to not see any difference between RGBHV, RGBS, and component with HDTV sources. Add more cables though and the potential is there for the slightest of possible improvements in image quality, though, in my experience, this is not something that the human eye will notice with video.
Standard 3 wire component video is the norm by which almost every receiver, television, and HD playback device uses these days. They are beginning to add HDMI/DVI to TVs and boxes, and (finally) receivers, but these are new and still seem to have some bugs related to them. If your cable box or DVD player only has component video output or DVI, then go ahead and hook it up component and take a look at it. Buying a high dollar converter to change it from component to RGBHV is not only a waste of money, it actually is redundant as every video display device already must convert any video received into RGBHV. Even lowly composite video (1 wire) is changed back into RGBHV by a display device before showing an image.
Don't over think the image quality and trying to achieve what isn't there. Begin FIRST with the highest quality source material which is HDTV video. Not DVD, not digital TV, but HD-Net or InHD video feeds from the cable/DSS companies. Then make your comparisons using whatever connections are available, which are most likely component, DVI, or HDMI.
S-Video and composite video do not have the overhead available to them to carry 1080i or 720p signals. So, these cables should never be used when you want to watch HDTV. I haven't watched anything over s-video or composite video in months - except my security cameras. Pretend those connections aren't even on your HD boxes unless you need them for something weird.
