huh, never heard of these two. Generally, you don't need a specific IDE for your Chip manufacturer – they are just ARM microcontrollers, and as long as your IDE is not restricted to a specific manufacturer (AtmelStudio probably is), they'll work with any MCU that is an ARM.
Now, of course, manufacturer versions of IDEs come with tools to generate initialization code, do things like estimate power usage and so on, but you can find these features to varying degrees in the big embedded IDEs, too.
There's actually quite some choice here. I'm kinda oldschool, and do my programming in the
OS Text editor of my choice, build and flash images with Makefiles and run GDB by hand for debugging, but I recon that's not necessarily the way to go for bigger projects.
So, the large competitors here are
- Keil (keil can, iirc, even be used free for STM32)
- IAR workshop
- ARM's own DS-5
and a lot of free tools, and I think it woul dbe worth mentioning
I'd go for Eclipse, if you've ever used that before. There's neat installation tutorials and it's got all the nice autocomplete, type inspection, debugging features already coming with it. Eclipse is a very "mighty" IDE platform, and is very broadly used for a lot of different targets, be it Java development, C++ for Servers, PHP for websites, or C for microcontrollers. It's very modular, so you get a pretty mature editor with very nice code tools, and nice debugger integration and so on. This particular Eclipse-based setup also comes with STM32 project templates, IIRC.
Basically, you can use any IDE that support GCC / GDB as compiler – the free (as in speech and beer, and both is good being free) GCC suite is practically the "native" compiler for the ARM architecture. You'll just have to configure your favorite IDE to use arm-none-eabi-gcc / -gdb instead of your host's default GCC and GDB binary :)