Which impacts DVD quality more, the choice of DVD program or the DVD writer?
IMHO, neither. A program used to burn a DVD should not affect DVD burn quality in terms of the data put on the disc, it should only affect what writing options / capabilities you have at your disposal. A better quality drive won’t necessarily burn a better quality of ones and zeros to the disc, but it should suffer fewer faults, last longer and be compatible with more media. Even choice of media should be of little consequence if the drive quality is good, or especially if write speed is reduced. I believe the one thing that will have the most impact on DVD quality is the choice of video compression while encoding the data prior to the burn. That being said, the best way to ensure purity of data is to make an exact copy, something that’s a little hard to do with long movies. At least, until double layer writers come out…