Well if you're using them for uploading to your YT channel, I would (in Sony Vegas) choose the MainConceppt AVC/AAC (mp4) & select one of the internet streaming choices. YT downgrades your video SOME, so I wouldn't go lower than the "Internet HD 1280x720 (720p)"
Also, it depends on whether you have issues with your internet if you have limits or if it's slow. If it's fast & pretty much unlimited, you probably won't need to worry that the file size might be too large, therefore you could select the "Internet HD 1920x1080 (1080p)" for a Really superb quality. Personally if it's a smaller video length, you can use the highest quality either the largest or the 1280 HD inet. If it's a long video I wouldn't do the 1080p, the upload could take a very long time. The "just right" (I'm thinking of Goldilocks & the 3 bears lol) is that internet HD 720p MP4.
I wouldn't; use the AVI, they tend to be way too large (taking up space when you save a rendered video on your computer). I would use the MP4 as mentioned above. It's great quality. I've put pretty much side by side, both an AVI next to an MP4, of the same render & the AVI was up to 3 times the size of the MP4 & they looked the same to me. If size does become an issue, I've heard the WMV format keeps a good quality but compresses the video quite well, to make the file size smaller. I've put also, side by side the same sizes of the same vid of an MP4 and the WMV (720p, 1280x720) & noticed the WMV was a bit washed out. If you hadn't had the MP4 next to it, you wouldn't have known it was though. I think the MP4 was much richer & made the WMV not look as good next to it.
So yes, for YT uploading the settings are already pre-done in SV, with the MP4 "internet HD 720p" & it's pretty much made for uploading using the internet (like to youtube) & this is what I would recommend. The quality is so great. Also, in the SV 12 pro, you can select "customize" right before hitting render after say choosing that "Inet HD 720p" & make even more changes. I usually do on the video tab, choosing "best" as the qualify before hitting render. The reason I wouldn't go lower than this is bc YT downgrades the quality just a bit. If you went lower, the quality could be sucky, which I see in YT all the time where when you click on the little wheel to choose a better quality (larger) there's no option to get a better view. :0
