Not a very good boxer, but one heck of a brawler. All in all, he's amongst the best in the deep 140 division. I have him in the top 4. If there weren't restrictions on the matchups that could be made, he'd easily be good enough to hold one of the four world titles.
A....His boxing as a whole is "B+" but he has a "fighters" mentality which is something you can't buy, train for or manufacture. Rios isn't the most polished fighter but he's got skills. It's when he has to bite down and impose his "will" over his opponent where he becomes champion material. Anyone who claims Rios is "C level" have NO understanding of the sweet science.
Dude is an "A." I'd take him to beat that bum Robert Guerrero, and according to all the *****s, he was an A+, p4p ATG.