Although I am rooting for S/H, I think S/M may have the slight edge because this is Aliona's third Olympics, and she's got both experience and hunger on her side. The cards were stacked against her in the last two Olympics because S/Z were by far the favorites in 2010, and the 2014 games were in Russia, which considers itself the "rightful home of Pairs" gold. So, this games may be Aliona's best shot at Gold, and she's stayed in the game precisely for that.
OTOH, S/H have likely been groomed to win this Gold for some years.
It could be an epic battle driven by two of skating's fierce female pairs skaters. Clean to clean, I've no idea which pair would have the edge if technical content is equal.