CNET tortured both the Apple iPhone 5 and the Samsung Galaxy S4 in a series of tests.
If you don't want to watch the whole video (or are on an iPhone or iPad which don't have support for Adobe Flash.. Yup, I know flash is supposed to be dead), the Samsung Galaxy S4 did a much better job of surviving the water immersion and drop tests. Both phones fare equally well in terms of screen scratch resistance, and neither one survived being run over by a truck.
In the end, premium aluminum is harder to make watertight, and does not far as well to to drop tests compare to plastic. But really, drop a Coke in can and a Coke in a PEP bottle, and you should already know that.