Mobi is a much simpler format than ePub, but it's pretty irrelevant these days. All current Amazon devices can use the enormously better "KF8" format, which will seamlessly convert to and from ePub. I've converted hundreds of books between ePub and KF8.
DRM has no bearing on the discussion. All these formats can use DRM or not; it's the publisher's choice.
Last edited by HarryT; 12-27-2012 at 02:59 AM.