I am on a PC using Studio 9 PE and processing MOV files from a Canon 5Dmk2 via CineForm conversion to an AVI. I've renedering out of Vegas at 720p and either the 30 or 24 fps.

My goal is to have the best looking computer playable/ Vimeo or YouTube HD video for my clients to view. I know that I have to render differently for SD (Mp2)

My "choices" in the dropdown for Mp4 is only Sony AVC which the manual says is "for rendering to PSP"

The way I see it if i'm not burning this to BR then I just want the best render settings to render for view on internet in best possible quality. what format is that??

(I won't know whether the viewer is on a Mac or a PC) so I've kind of leaned toward Vimeo or YouTube distribution so clients can point friends to it to share.

So what render format?

You have a few more options than that...go take a look...

initial format??? your screenshot is showing templates for the Sony MP4 format......

Check this out: TUTORIALS: Vimeo HD exporting guides from many editors in the Help Forum on Vimeo (http://vimeo.com/forums/topic:3671) . But it's not necessarily correct anymore, check Vimeo and Youtube for the formats they currently prefer and use those (from memory Vimeo now prefers 1080p mpg4).