Dave Dugdale has published a quick test between Magic Lantern raw with green screen vs H.264:
According to him:
The raw video keys a lot easier than the h.264 version, you can get a much cleaner matte. But the final key for both look pretty good.
Notice the moire patterns on ML raw with my shirt that doesn’t happen on my h.264 shirt. Actually now that I have uploaded it here on Vimeo you can’t see the patterns anymore.