I'm really not a good judge of who might be stronger, unless one guy is obviously bigger than the other.
Of course, I suppose I'd be a little biased toward Sonny, but I think in the case of a physical fight, a quick temper like Sonny's would be an advantage with the adrenelen pumping and all. Of course to most of us Carlo wasn't a likeable character, and seeing him get the s**t beaten out of him somehow seemed like a case of "just desserts".
TIS