I don't know much about gravley recently but used a walk behind like your dads about 15 years ago and loved it It was a tank. It took all kinds of abuse.
Right now I cut and acre and a quarter and use a Exmark CT 48" and love it. It is a tank and I bet will be my last mower. It also is fast as heck. I cut my grass in less than and 1 hour. What ever mower you get you ought to get a striper kit for it. It really makes the lawn look nice.