Thanks Cortex!
I found some ARM compilers benchmarks. It seems that Keil and IAR achieve similar results of code size and speed optimizations.
I have worked with IAR for Renesas H8 microcontrollers and it would be easier for me to use IAR for ARM's. But I saw that Keil has RTOS included in the package and they have libraries for TCP/IP and file systems.
What do you think, what is better, to use Keil with its RTOS and TCP/IP or to use IAR with third-party RTOS & TCP/IP stack (for example uCOS-II + lwIP)?