I guess it depends on what you are going to do with them really.
First off, since I assume this is regarding the axles that are under your Superduty, the other choice up front is a Dana 50. It has a limited selection for regearing...or at least it did. Not only that, but it is simply a weaker axle as far as shafts and ring gear.
The main reason that most people want the 60 is the same reason that they are put under 1 ton truck in the first place...strength.
They are quite popular with the off-road crowd...larger tires and more engine on the stock axles of most vehicles makes from lots of broken parts. The 60 is a step up. Many have now gone past 60s to Rockwells from the larger military 6x6 trucks, but there are still looking to run 60s.
Then you have the people that think they NEED the strength of a 60, mostly because a bunch of other people have them.
Then you get into the different 60 variants...and there are several. Some are more desireable than others. That's more discussion than there is room here.
Personally, I have one that is going under my Jeep this winter...I HOPE...