I can’t pretend I know anything about Vegas, but I know a little about HiDef delivery.
I assume that since you want to play this back on an HD system that you have a Blue Ray burner. There are several codecs supported by the Blu-ray format. MPEG-2 and h.264 are two of them. If Vegas supports rendering out as both then the choice as to which codec to use can be determined by content. Some content comes out better with one codec than with another and some applications render better to one than to another. Only testing will tell.
