I've prepped the naked steel of many frames by both these builders and they are both first rate. I see no reason to render opinions placing one over the other.
In working with Confente, I witnessed his technique and work habits first hand. I can make comparisons of that to the dozen or more builders I have seen work.. Mario's speed, precision and fastidiousness were incomparable. Everything place, no wasted motions, focused, a hard worker in full command of his craft. Amazing to watch. I've seen others who create a fine product, but do so inefficiently, at a casual pace and in a slovenly environment. Not that this matters to the end consumer, but in the question of what makes a great builder I'd say that these attributes are important. Mario had the skill and discipline to bring excellent value and/or profitability to full time building of artisan frames. Also, as was certainly so in my case, his skill was a lasting inspiration.
I've never met Ron Cooper, but judging by the fine work and long, full time building career, I suspect Ron Cooper has many or all of these attributes.
JFC
CyclArtist
Vista, CA