[co9ol]

If you're going to have to re-encode again while authorizing the DVD might as well go huge. However, if you won't have to re-encode the video before burning the DVD go the biggest you can go before hitting 4 GB. Most programs have a "estimated file size" when selecting the bit-rate, use that.

This is assuming that you only want to fit one video file on the DVD...

P.S. Stick to MPEG2 for DVDs