I interviewed at all of them except Ohio State. Liked all of them, and the residents seemed happy in all of them. With the exception of WashU, very clinically oriented programs. Probably more about location than anything else amongst the more clinical places. WashU is an extra year which is a positive or negative according to personal preference. Of the ones you listed, my two favorites were probably St. Louis and Little Rock, based primarily on proximity to my hometown. WashU has a lot of opportunity and happy residents in a bigtime academic center, which might offer a unique learning experience.
Arkansas is smaller but enjoys a strong reputation within the region. Although it is a clinically oriented program it does offer some of the academic opportunity afforded by a university center. Little Rock has some really, really rough parts so you probably get plenty of gun/knife club. Arkansas is a poor but physically beautiful state, and their residents do very well moonlighting and get great jobs.
Seems like you can go pretty much where you want from most accredited residencies, so for me it comes down to location, gut feeling, and finer details. I think all of them have solid reputations, although WashU is still creating a name for itself more than the others (having said that, its really high on my list).
so whatever you (or your son?) liked best, it is most likely a great choice.