I made several pairs of DVDs, each recorded on the same machine, and reproduced on the same VCR, but one using S-Video, the other using composite. I asked some friends to rate them, not knowing which was which, just saying which DVD looked better to them. (A "blind" study.) The conclusions I came to were 1) my sample size was insufficient to make any REAL conclusions, and 2) It was split evenly, and randomly as to what interface was preferred. No one person consistently chose one over the other, and there was no overall trend preferring one to the other.
Using my 53 inch Panasonic as a display, and my EH50 as a playback machine, there was no obvious preference in the finished DVDs of one connection over the other. With all that said, I highly recommend you do both and decide for yourself. I know you said you cannot do it, but without an actual test using your equipment and cables, ann I can do is guess.
Use the best playback machine and the best cables you can get your hands on. I have seen poor quality S-Video cables corrupt the signal more than a good composite cable. It is all in the details. Keep your cable runs away from possible noise sources too. I have seen that overwhelmingly degrade an otherwise good signal.