Sonny would serve best as a capo or underboss having someone over him to reel in his anger while being able to put Sonny's talents to good use.
I wonder how Sonny as underboss and Mike as boss would have worked out. I can imagine friction with Sonny taking orders from his little brother but I also think that Sonny could have helped to keep Fredo in line and he wouldn't have had that unfortunate boating accident.
He didn't seem to be that great a capo when he was under his father's authority. He was bored silly when Vito was doling out favors on Connie's wedding day, he spoke out of turn during the Sllozzo meeting, and he was screing a bridesmaid with Vito's tacit knowledge, when he should have been in the meting with Johnny Fontaine.
I don't see him as working well under Michael, first because of the older brother thing, but more importantly unlike Michael he lacked the ability to wait until the right moment to strike, and when he struck it was always at his real enemies. If Sonny were alive in GF II he would have wanted to kill Pentangeli.
I do agree he would have handled Fredo better....but then anyone xould have handled Fredo better than Michael did.
