I wish Sony would rename the display/render options because they are misleading with most newbies obviously picking "best" since the name implies its better. It can be... but not always and most of the time not necessary or worth the extra time.

The difference between "good" and "best" refers to how things get handled. Example: Assume you're using pan/crop or applying one of the filters that changes hue, anything where pixels are getting added or changed.. Vegas is similar to still image applications like Photoshop it that it has choices of what method is uses to interpolate pixels. That's just a fancy word for saying how the application adjusts and in the case of Vegas renders the output.

If you select "good" then something called bilinear interpolation is used. What's to the top, bottom, left and right are used as the basis to apply the adjustment in hue.

If you select "best" then bicubic interpolation is used. In addition to looking at the pixels to the top, bottom, right and left it also looks at the diagonal direction as well and usually a weighted average is applied.

All the extra caculations can take a good deal of extra time in rendering. Most of time you don't need it and won't see much if any real difference. There are exceptions of course. So if you're doing mission critical, try a small render with both methods.

Generally, if your source material has lots of solid colors and few if any still images inbedded, stick with good. Its what Sony has always suggested. If you have a lot of still images of very high quality or source material with lots of graduation or where something must remain as close as possible to the source hue, then and only then use best. Otherwise (in my opinion) the rendering time which can double isn't worth the effort and you probably won't see much of a difference.