This is the first I've heard of the EPL. I'd love to hear someone elaborate on why it's listed as the "best copyleft license", specifically with regard to the GPL.
The EPL is roughly in the middle of MPL and LGPL in terms of copyleft scope. MPL requires per-'file' source sharing. EPL requires per-'module' source sharing. LGPL requires per-'module' source sharing and separating the module to permit the user to use/replace it without additional restrictions.
The one downside that EPL has is that, unlike MPL (without "Incompatible With Secondary Licenses" notice) or LGPL, it is incompatible with the GPL-family of licenses. It specifies different conditions for providing the source code and has a governing law clause (New York).
It is popular in the Java ecosystem (Eclipse, Clojure, etc).
