My release package for mono does not need silverlight and does not give that webpart error at least on the latest mono.
The best version of mono is always the newest, for the very best I recommend you build mono from svn then if you find bugs in mono you can report them and get the fix and rebuild. Unfortunately there are bugs in mono, it keeps getting better but it still has bugs. I do not test new versions of mojoportal on old versions of mono so I don't know how well it can work with mono 1.9.1
Hope it helps,
Joe