I think Z is just being a bit overzealous, mainly brought out by someone that repeatedly would tell every new user that Mobipocket was the best because it was the most widely supported. Strange how things turn and the same individual criticizes a person for doing what they did.
The best format is certainly the best format that displays on a given users device + has features (cross-compatibility, ease of conversion, etc.) that the user holds valuable. I personally think that epub has the best all around qualities for an archival format.
-MJ