How do ppl like freertos vs zephyr vs nuttx? Have any real comparisons been done? Both on flexibility (platform support and code portability... I know... Nuttx

How do ppl like freertos vs zephyr vs nuttx? Have any real comparisons been done? Both on flexibility (platform support and code portability... I know... Nuttx, POSIX) and performance (interrupts, context switching, etc) I've been looking at zephyr which seems all around better, albeit a bit less mature. I have no hard data though... Hence this question.