I can see why Putin would release such data, but he threatened (as I recall) to release them as such. I don’t see why he would use a third party conduit for the release.
One of the problems with figuring out who released this, is to define the number of people who are enemies of the Clintons, for both personal and policy reasons. That number is probably quite staggering, and some of great influence and resources. According to Guccifer, at least ten other entities hacked her effectively undefended emails.
Wikileaks is more credible than the National Enquirer.