I've never heard of the Masters in General Management so I couldn't tell you academically the difference between the two, but as a credential, at least in the US, the MBA (and the programs that grant it) is very well known while with the MGM you'd probably have to do a little more explaining to people/employers what skills you have as a result. You may also find yourself shut out of certain opportunities (I'm thinking in banking or consulting) where they specifically want the MBA credential. Again this is probably US specific so if you're elsewhere you can just ignore me.