I have compared the Xperia S and the One S on different things and you can now watch my videos.
Design comparison with the Desire HD:
I prefer the One S because it's thinner and more pleasant
The screen is better on the Xperia S
8Mpx for the One S, 12Mpx for the Xperia S. But they are equal, with a preference for the One S because of shooting in the dark and against the light
Benchmark & UI test:
You have to see that to say which one you prefer.
One S chipset is for me better but very very better xD