I have been doing some testing of the component video signal quality output by various PlayStation 2 models. The short summary: the earliest fat PS2 console (model SCPH-30003, V3) has significantly better image quality than later consoles.
[Edit to add (see follow-up posting below): the stripes in the image from the later consoles are only visible in PAL (576i) or 576p modes. They don't seem to show up in NTSC or 480p mode.]
Either the poorer image quality of later consoles is not noticeable when the console is connected via composite video or RGB SCART to a CRT television, or the problem is only present when using component video (YPbPr), not RGB or composite video. While the poorer output from later consoles might not be noticeable on CRT TVs, it will may be noticeable on modern LCD/plasma TVs and when capturing video to your computer. When capturing video, apart from the poorer quality due to stripes on the display, the stripes will decrease the effectiveness of video compression codecs (like AVC/H.264). So if you're creating your own PS2 game-play videos, I suggest you use an original SCPH-30003 console.
What causes the poorer image quality in later consoles? A large part is probably because of the increased level of integration. Early consoles contain separate EE (CPU) and GS (graphics) chips, so there is likely to be less noise/interference to the video signal from the EE. That's not the only reason though. The SCPH-30003R still contains separate EE and GS chips but its video quality is slightly worse than the SCPH-30003. Poorer-quality circuit board layout may also be a factor. Perhaps the first SCPH-3000x consoles had a PCB with more layers, allowing the video signals to be routed with less interference from other signal lines?
Using an AVerMedia C927 HD capture ExpressCard, I grabbed some frames from several models of PlayStation 2 console. The consoles were connected via component video (YPbPr, 576i).
I would like to obtain SCPH-3500x, SCPH-5000x, SCPH-700xx, SCPH-7900x and SCPH-9000x consoles to test them as well. I do not have the Japan-only SCPH-10000 or SCPH-15000 consoles, but I suspect their video quality will be at least as good as the SCPH-30003.
I have attached some example images below, for SCPH-30003 and SCPH-77003. You can download an archive with more images from each different console model (~19.8MB) from here (4shared) or here (multiupload).
SCPH-30003 S/N B07xxxxx (V3 console)
The early V3 console has 10 screws on the underside. This console has easily the best video quality. All other consoles I tested are noticeably worse. There are no stripes in the picture.
SCPH-30003R S/N B28xxxxx (V6 console)
Stripes are most noticeable in the Open PS2 Loader yellow, green and dark green screens. There is a noticeable difference between the Browser pictures for SCPH-30003R and SCPH-30003. Faint stripes on the other pictures.
SCPH-39003 S/N B47xxxxx, B52xxxxx (V7 consoles)
The stripes are thinner and more noticeable than with the SCPH-30003R, e.g. compare the OPL orange and purple images, and the Asterix XXL2 title screen.
SCPH-75003 S/N FB62xxxxx (V14 console)
Stripes are of similar severity to SCPH-39003. On some screens though, they are less apparent, e.g. the OPL orange, purple and yellow screens.
SCPH-77003 S/N FB78xxxxx (V15 console)
Stripes are slightly worse than for the SCPH-75003 console.