Hi Victor, I have some first hand experience with all three.
"meaningful ones focus more on strength? Flexibility? Flow? Muscle tightness? Breathing? Becoming pain free?.... "
They all approach the above in one way or another. As for pro's and con's there are enough of those lists on various threads and I find they all come back to the persons experience with that form of training and honestly my "personal" experience is not your experience and as such its not going to be meaningful for you. There are allot of threads on this forum where people begin with good intentions of sharing info and then get into shouting matches regarding the best this or the best that. Suffice to say, describing these things and their value is allot like telling you what Thai food tastes like, all the writing in the world won't mean anything to you until you taste it for yourself.
All that having been said, I am sure you have some idea of what each of those health systems is about. They all have something to offer depending on your goals. If you are looking for something that compliments the combative arts well, then dig a bit into Sonnons stuff. The health system that is a part of R.O.S.S has many interesting exercises, breathing methods and movement drills that have a direct performance impact on your combative skill.
Hope this was somehow helpful.