I've used IAR extensively but support was not great. When I found a bug and explained what happened I received back the standard question to create a small example which shows the bug. So I did and sent it in. After that I never heard anything again. IAR also used to have a very bad user forum with all tools mixed. Nowadays they have nothing. My recommendation: Also have a look at the existence of a good user forum for the tool.

A plus for IAR is that the linker can generate a checksum/crc over the generated code and store it inside. This is good for bootloaders or selftesting. Another plus is that it can generate GNU make dependency rules which is nice if you don't want to use the IDE.

If you intend to use libraries for which you have no source access, make sure your compiler can use them.