All three have their place, and all three have advantages.
I assume that everyone here knows the advantages of International Ballroom when it comes to technique. If you want to look really good, or if you want to compete, this is for you.
Round Dancing, on the other hand, allows people to dance figures, (Pretty much the same figures that the top competitors use in their competition.), and routines that they might never master in Ballroom. Dances are Choreographed by some of the best dancers in the country, and shared with everyone, without charge.
Round Dancing is very inexpensive, and they use great music. The routines that last, are very good.
Then we come to Social Dancing. Social dancing is often looked down on, but it is the only dance form where leading and following is absolutely necessary. You must lead if the person you are dancing with is an unknown tallent. You have no idea what the lady knows, or how much she has been taught. If you happen to have a routine, she may never have seen it.
It is necessary to start off with very easy figures, and then experiment until you find out what she can do.
My opinion is that the very best dancers should explore all three.
I think one can benefit from using the best qualities of each dance form.