ProRes would require the end user to download an additional codec and install it beforehand. H.264 can be played back right away. Think of your user experience as well.
I figure that out the hard way. The prores took an hour to upload and when it finished, it was rejected. by vimeo. I ended up doing H.264 at 800kbps. Turned out pretty nicely. I was just wondering if there was any better option.