Ive seen horn and wood handled kukris over 100 years old. I wouldn't worry about the failure of either in the field. If horn is going to crack it usually does early on in ownership. Once fixed it's pretty darn tough. Wood is probably the easiest to work with out of the two.
I however have developed a polishing routine for my horn handled kukris and I have really come to love the look of horn again.
I would say that without qualifying, wood would be the quantifiable answer. It's easier to work with, seal, and repair if need be. That's not to say that horn or bone is a bad choice. Both seem more than stable. However, I tent gravitate toward wood (mostly for looks and "feel").
The bone handled khuks and knives I have seem a little more fragile than the horn or the wood, although I don't have any real choppers with the bone handle. They seem to have a more hollow feel.
As far as wood and horn, I can't tell much of a difference strength wise, but I have had substantial cracking of horn (my own fault) because of dry conditions while the wood never has, even though it can also crack under dry conditions.
I enjoy the look and feel of bone over wood however it comes with a price in my area. It is so dry that I have to spend more maintenance time on bone handles and ivory - less time on wood. I have never tested the durability factor between the two.
My M43 which saw such extensive use has a horn handle, it has held up wonderfully with very hard use outdoors in all seasons. All I ever did to maintain it was put some oil on it occasionally.
However to qualify things this is on an M43 with a Chiruwa style handle, performance may differ with the traditional handles.
I chose horn over wood only because of a lower friction coefficient than wood (perceived by me before having used both), this was a concern because I could forsee some long chopping sessions ahead. The reality after having used both is that there is very little difference in use. The wood handles also require some care, a little oil now and then, and are easier and more forgiving to modify to the users hand. Both stand up amazingly well.
I have both, and must say that the wood handle gives more grip compared to the later. While it is much prettier, you can't tell because the non wood handle is now wrapped in hockey tape for the safety of a secure grip, something I have not found needed with the wood handle.
I order my Khukri in villager finish because they are used hard and the polished finish would drive me crazy trying to keep a tool mirror finished! Any future purchases will be wood handled, unless I were to have a wall hanger, then the shiny finish and bone/horn handle would be a must.
My oh my... After buying two BAS, two GRS, and having my third BAS on the way soon, I must admit: Yes, I have become a Khukuri junkie.
Now, I am actually drooling over the 18 inch WWII. My question is if someone knows if one type of handle – horn or wood – was more common on the WWII issue, historically speaking?