S-video is the min. I would use. Component (NOT COMPOSITE) is next best. Since you mentioned Digital Light Processing (aka digital fixed resolution panel) you're best option would be DVI/HMDI. If you are using Direct TV, Digital Cable or DVDs, your source material is in a digital format. Your display is also Digital so it would be best to feed it a digital signal.
Composite, S video and component video are all analog cables. In this scenario, the source component (dvd player, STB) must convert the digital signal to analog and send it to the DLP display. Since the DLP display wants to see a digital signal it must convert it back to digital. The D/A and then A/D processing degrades the signal. If you have a Dvd player or STB with an HMDI or DVI output, you can keep the signal digital the whole way. You'll get a much improved picture (one that has not been degraded and is more accurate).
YMMV
Bomber