Bit late to the discussion I know, but thought i would add my 2c as well.
At work we have recently shifted from Keil to Atollic Truestudio.
While keil is great, their v5 compiler was having more and more issues with newer ST processors that we are looking to use, eg F3 and F7 series. While their new v6 compiler (based on llvm) looks great, it would have required re-starting our support subscription, which is as expensive as all heck.
We looked around and ended up switching to what i had been using at home for quite a while: Truestudio.
It's a great IDE. It's basically Eclipse + GCC + GDB, but with a few nice ide additions. Some optimisations and changes to how they use the CDT build system and also much better/more reliable gdb support, especially for trace debugging etc. It also works great with the STMcube.
It's also much easier to setup, just install and go.
It does have a few downsides however. but for us they were less of an impact than the downsides of keil.
Oh and as others have mentioned, the free/lite version has no code size limitations. The only real limits are they restrict some/most of the extra advanced debugging functionality that things like standard eclipse+gcc dont offer anyway.