Frankly, I agree with you about Dany. The Targarion line is a legitimate claim, and most compelling. Plus, if Dany can bring an army back to Westeros and kick some ass, she doubles her claim, both as deposed family *and* as conqueror.
Just a guess, so no spoiler tags needed, but I think that's the ultimate fate of the Westeros crown in the end. And there are a lot of alternate possibilities, too.