I found that uploading 1080p produces the best “look” of my work, but man it takes a long time when you live at the end of the DSL circuit. Because of this I tried 720P and finally settled on 480p, but am not happy with the quality, though adequate for the audience (church members catching a service they missed). I do think the uploaded format makes a difference. I found that if I uploaded .mov files the upload was faster and the conversion was fast and the quality is great at 720 or 1080. This is coming from a Sony consumer camcorder.
That said… what SargeHero said was very true. Garbage In, Garbage Out. The big time players have some big time equipment.
