Most Helpful Guy
There is no really existing convention for it. Each couple decided on their own what works for them. Some dont take a new last name, some combine them, some pick a completely new last name. For my fiancé and I the decision was made because only about 100 people in the world have his last name so I decided to take it. From my point of view it's like and endangered species I'm protecting.
Some couples pick the one that they think sounds better or is easier to pronounce, or is more unique.
It's not often picked by "who's the man" because there isn't always a clear cut answer to that and it isn't as important as other factors in deciding on a name.
So long answer shortened, there is no one way we decide.0