My YouTube videos look pretty darn good, but after YT converts them they’re never going to look like the originals. My experience is that if you start off with good quality (not a cheap crap video camera) your video will not lose too much quality.
In Vegas 12, I use the render template ‘video for internet 1080’, which is the MainConcept render option. I then edit the template, enabling two-pass and I raise the average and maximum bit rates to 25,000,000 and 50,000,000. This will give you longer than average video render times. With the above settings my YouTube clips look really good.
Dave