Well even compared to the Galaxy S3 HD SAMOLED, Xperia S screen is way sharper and more vibrant. So I am sure compared to the RAZR MAXX screen which is even worse than Galaxy S2 screen, the difference will be significant.
But anyway, if you haven't used a 720p screen then get the Razr Maxx, you will love the screen as its still an above average screen. And as its OLED, contrast is great.
But if you are comparing both as phones, the Xperia S is superior in everything but battery life. So if battery life is key, Razr MAxx hands down should be your choice.
After the ICS update my Xperia S battery performance is decent. 1 day is easily manageable with heavy usage. With light-moderate usage even 2 days is not tough to achieve.