You can't beat ChibiOS if you want working peripherals out of the box. The license isn't necessarily an issue, because it permits you to link your proprietary code against it, but if you need to make any modifications to ChibiOS itself those must be open-source. FreeRTOS also uses a copy-left license so migrating to that wouldn't help. However both OSes have a commercial license option available.
Personally, I chose to ditch ChibiOS because of the license. I'm currently using CoOS (from CooCox) which is a decent core but does not have any peripheral drivers, so I had to write my own. It is BSD licensed so you can use it in commercial projects without issue. As for the OS itself, it works well enough but it's not amazing. I found a race condition in semaphores that I had to patch, but I haven't pulled in any new code from upstream for a year or two so it's probably been fixed by now.