It's a matter of max throughput. The diverging diamonds is great when we are talking many lanes in all directions anyway, like in highway interchanges. The roun

It's a matter of max throughput. The diverging diamonds is great when we are talking many lanes in all directions anyway, like in highway interchanges. The roundabout wins when max throughput is not the goal, and some of its side properties, like some mild traffic calming and better interactions with pedestrians come into effect. They aren't really in competition with each other under most circumstances. It's like comparing bicycles and trains for transportation.