This is a name where I'd definitely spell it phonetically correctly rather than worry about what's actually correct. (I'd be more concerned about it being mispronounced all the time than I would about someone thinking I was "trendy".. and no one in the real world is going to think that).
Fortunately Madalyn and Madelyn are correct spelling options (even if they are Americanized), so even if you're concerned about it being an incorrect variation, it isn't, so you're alright.
But I would pronounced the other two as Mad-uh-line.. even if they can be pronounced differently, I wouldn't. When I read it, I see Mad-uh-line.