Define "better." The word means different things to different people in different settings.
5.9 Cummins and 7.3 IH-Ford have the same longevity under equal care and usage. But the Cummins will give better fuel mileage - from any I know of.
From an engineering perspective - the Cummins is absolutely built heavier then the Ford-IH 7.3. But who cares if they both can outlast the trucks they are in?
I still have my 92 Dodge 4WD extended-cab, long-box, 5.9 turbo-intercooled. 3.50 axles and Getrag 5 speed manual.
I also have a 94 Ford 4WD extended-cab, long-box, 7.3 IDI turbo. 4.10 axles and E40D trans (auto with lockup and OD).
The Dodge pulls hills better with a trailer and always gets 2-3 MPG better then the Ford. Considering it has 3.50 axles whereas the Ford has 4.10s the ability to pull better is impressive. The Dodge always gets better MPGs, loaded or empty. Granted that my 7.3 is not a later DI Powerstroke 7.3 but I've used a few. More pulling power and same MPGs, more-or-less.
If I had to say which of my two trucks were "better" . . . I'd say the Dodge-Cummins is "better" for hard pulling and economy. The Ford is "better" for comfort. It rides and handles like a Cadillac and the Dodge rides like a Sherman tank.