I haven't seen any hard numbers, but from my subjective experience and anecdotal data I'd say Soundcloud is closer to Youtube than Vimeo for a number of reasons.
Vimeo isn't focused on the social aspect. It's a platform for pros to share their content in hi quality which is the only reason these pros aren't using Youtube in the first place.
Soundcloud doesn't pretend to be a service for pros. Otherwise why stream at 128kpbs and offer such meager and ridiculously priced plans? Also no pro tools for distribution or even selling music like Bandcamp does.
Soundcloud is focused on the community and social experience much like Youtube or even IMGUR. This is why I believe it hasn't been able to monetize its efforts.
Either Soundcloud starts monetizing with ads or it becomes a real platform for pros.