Don't follow any of the previous tutorials, they're all so so wrong. I haven't used Vegas in years now so I don't know if all these options are in the old versions of Vegas, but if you've got Teamviewer I'll set it up for you based on what I use in other applications
EDIT: The reason I can't just post a preset is because a lot of things change between different versions of Sony Vegas, making it hard to recommend one preset for everyone. For example, it's debatable whether you should use Mainconcept AVC instead of Sony AVC depending on your version of Sony Vegas. They both render h.264, but the options for each both change depending on which version of Vegas you have.
Everything in Vegas 10 would lead you to believe that Sony AVC can only render in constant bit-rate, but it actually renders using a variable bit rate based on what you've chosen, with a max bitrate of 16mbps. In Vegas 11 the 'Internet' templates are switched from Sony AVC to Mainconcept AVC, there's many things to take into consideration. The best version of Vegas is obviously Vegas 11, and rendering at high quality is also much easier with this version.
The worst thing you can do is render to MeGUI or a similar type of program. Total waste of time for minimal improvement in quality. This isn't even an issue with other editing programs (Premiere Pro, FCP, Avid etc), as they're all capable of rendering better files than Sony Vegas. The best advice I can give to anyone is to do their research; don't listen to random tutorials on YouTube, seek out factual data about encoding and then apply that to the program you're using. In other words, only listen to professionals.
