I agree with mhotovec. I have the Razr Maxx and would love to switch it for a new phone. But to compare the Maxx to S3,
It has the same type of screen (Super AMOLED) which is darker than normal LED. I personally hate it. Maxx has 4.3 inch screen with 256 PPI, and S3 has 4.8 inch screen with 306 PPI.
S3 has a Gyroscope, and you can use a 64GB Micro SD card, and it supports DLNA.
Maxx has HDMI (which i personally never used)
S3 has TouchWiz while Maxx has Motoblur.
Both are dual core.
No major differences. It really comes down to how much you have to pay to switch, and whether you like Maxx's screen or want a larger screen and slightly better one, prefer TouchWiz or Motoblur, if you like the physical style of S3 more, or if you just want something different.