Avoid ST at all costs in my experience. Their documentation is terrible. They never acknowledge hardware errata even after clear evidence of it. They’re not a company with a solid engineering culture imo
More so for Microchip than Atmel --- it's pretty common to find on some of their newer and more complex parts a ton of errata, among which there are some extremely "WTF!?" ones like "feature X does not work at all".
I will say that STM has definitely released better tools that make it much easier to get designs up and running (STM32Cube specifically).