At the moment I am using Keil with one of the STM32 cheap development boards. I have the free license (well, until Feb 2018) for the STM32F0x and L0x chips. I am using this becuse I am new to the system and a really cheap way of learning the chip.
After I am up to scratch with the systems, I plan to design boards/firmware for other processors apart from the L0x and F0x chips. I find the Keil to be quite good, but a bit pricey for the STM32 license, about $2.5k'sh. I have been looking around, and found VisualGDB, which is a lot cheaper price. I have also found forums saying its a good product, but doesnt pack the final code as good as Keil. Anyone give me their experience, or perhaps another developement kit?