Jigged bone will crack over a long time without expending minor care. (A nice soak in mineral or baby oil a couple of times a year does the trick for me. I try to accomplish the tasks between Spring and Summer and Fall and Winter)
That being said I carry a jigged bone equal end that was made before 1915 now and then. The bone looks and ages great with that minor care and there is not an evident crack.
Stacked leather will provide for a better initial grip (when new), but is more subject to different problems. I have heard of folks who have had nasty troubles with some type of insect or critter that pretty much destroyed them and some chemicals.
If I was trying to choose between the two, the environment that I would be using the knife in most of the time would come into play.
If I was in a damp or chemical environment most of the time, I would choose the bone over the leather (big time). If the environment was more arid, I would choose the leather over the bone (giving the leather a slight edge for gripiness) and make sure to seal it with type of wax or even polish to keep those leather consuming critters out.
Just my thoughts, I am sure there will be others.