Here's a bit of narrative to accompany my screenshot comparison, just to give some pointers as to what you should be looking at. (It would also be beneficial if you could ensure that your monitor is correctly calibrated when making comparisons.)

Shot 1: Tonality check (#1)
The blackness of space should be black, not a shade of grey, and the stars should be clear bright spots. Also check that the ships are the correct "temperature" of grey with no colour cast, and look out for dot crawl artefacts on the laserbolts.

Shot 2: Hue check
Incorrect hue is most noticable on skin tones. Check that the face is a natural skin tone, and not too yellow (EditDroid?) or too purple (ISOMIX?).

Shot 3: Chroma subsampling check
Look at the raw DVD screenshot, as it doesn't show up so well on the resized image. Check the extremities of Artoo's red light. The TR47 and ISOMIX versions show the artefacts associated with a DV capture.

Shot 4: Tonality Check (#2)
As well as the black of Vader's cloak, and the white of the roof lights, this shot displays all the midtones in between. The Farsight version shows what happens when the white level (contrast) is set far too high. Also look for the halos to the left of Vader on the Moth3r version, caused by setting sharpness too high.

Shot 5: Detail Check
Examine very fine detail in this shot, such as the appendages of the droid in the centre of the picture. Fine detail appears blurred in the Dr Gonzo transfer.

Shot 6: Dot crawl test
Look at the edges of the red sun in Tatooine's sky. The EditDroid version gives a very good example of what the dot-crawl looks like.