Generally, tga is preferred, but png is a close second. The compression of png can sometimes mess with colors. Somewhere in a thread here, you can find some stills posted, but it's about a year or so old.
you're correct: tif requires quicktime to read the file format, so you'll want to avoid tif's where you can.
I started using .png about 2 yrs ago after some jpegs had some problems with jittering. Reduce interlace flicker had no effect. The .pngs have been very steady. I also use .tga sometimes but not often. I haven't found a way to get Windows 2000 to show me a thumbnail of .tga files when using explorer. That comes in handy with .png and other formats.
> if you go on the png website - even they say dont use png's for high quality photos ...
I think this is a file size issue, not a quality issue. PNG uncompressed format is as good as bmp, psd or pic and always superior to jpg in term of quality.. File size aside, there is no reason not to use it in Vegas IMO. And transparency is cleanly and perfectly managed for 32 bits files.
A vaslty underused application of PNG format is in color indexed images for the web. For many reasons, it is a really better, more flexible and efficient format than gif, but it slowly gained acceptation at first as a supported format in IE (shame on MS for that!). The same is true for jpg2000 format but that's another story...
AFAIK there is no viewer that shows thumbnails of all still/video file formats without sometimes crashing in the attempt. Every one I've tried and I've tried everything from high end stuff to shareware to freeware stumble on one or more formats every once in awhile. If somebody knows of one that can show various types of AVI, MPEG including DivX, Real and other common video types, without crashing in attempting to open them, tell us about it.
Another issue is of course many vids start out fading in from black, which makes the thumbnail useless, unless you like a totally black frame as a thumbnail. While a pain to keep up I open whatever in Vegas, then make a thumbnail of a representative frame, then save in a database. I mentioed the one I use several times already in other threads.
Well, I'm sure that those with more experience have very valid reasons for stating otherwise, but I'm surprised that nobody's yet pointed out that the manual specifically recommends png files.