It doesn't matter!
For straight cuts Vegas does nothing to the video. If you truly want kickass quality then it starts well before the light hits the lens, the next most important thing is the lens, then the CCDs and then the encoding system used to write the image to the tape.
All of this will have WAY more impact on your image than anything Vegas or any editing system can do.
Unless you're rescaling the image rendering at Best is as good as it gets. Of course in Vegas there's a lot you can do to improve your image. But for really kickass stuff read what I was saying before. The more you find it necessary to tweak your image in post the less chance it's got of being kickass. Vegas can do as good if not better job than any NLE of turning Good video into Great video, trying to turn Poor video into Good video is very hard. Same goes for audio and it's a lot cheaper to record and produce good audio than video and that's at least 60% of the show.
Bob.
Assuming you're fairly new to video, sorry, if you're not, once your past the creation phase and the importance of the things Bob mentioned that effects your inital capturing of the video, the camera, lighting, etc., the next thing that probably effects quality most is what you use to render the video which if you're doing editing or adding effects is determined by how much or if you compress the source and what file type you pick, if not not you transcode, (change the source file type to another) or change frame size, rate, things like that.
Give more details on WHAT KIND of video you're making, will it be for a DVD, only played off a computer, steamed off the web, whatever, then you'll get more specifc responses.