The STM32F091RCT featured on the Nucleo-F091RC is pretty much what I need. It's not too expensive, supports USB, nice fast ADC, and has a CAN channel I'd like to use one day.
If you intend to continue with ST, there is a number of online courses that explain the use of CubeMX and the HAL, e.g.:
If you don't like System Workbench (I'm not fond of Eclipse based tools either), specifically for ST F0 and L0 MCUs, the Keil development environment is
free without code size limitation.
CubeMX can directly generate Keil MDK projects.
I happen to like
Visual Studio Community (free as in beer) +
VisualGDB (not free, but not expensive): it just works for me, VS is an excellent development environment and VGBD also supports a number of other vendors' MCUs (ST is one of the better supported). Plenty of tutorials, including importing CubeMX generated projects.
In the Cube, in addition to the HAL, CMSIS and other drivers/middlewares, there are tons of example code for the Nucleo, Disco and Eval boards, providing a good insight on HAL use.
On a completely different note, danadak, ebclr and dgtl have suggested Cypress PSoC, which is a really interesting alternative.
Cheap boards, decent
IDE (but one is 100% bound to it for the HW definition part) and great fun.
The peripheral library API is simple and clear, and one can design their own specialized HW: e.g. I recently used it for a reciprocal frequency meter (a couple of evenings), and to make a test harness for a simple ATtiny based project (a couple of hours).
All of the above IMHO, YMMV etc. etc.: this is an hobby for me, though I work with SW.