As usual, I agree with Yvsa: "it all comes down to personal preferences."
I don't think you have to be afraid of either. Horn is definitely more water-resistant than wood, and wood can have a somewhat more grippy surface, but both work just fine by me. More people around here already know how to take care of wood than of horn, but I've had no problems with the horn. I leave them all out in the garage so they don't tend to undergo a lot of temp and humidity shock and I rub hooflex into the horn every now and then. I've had no cracking at all.
Now the leather can be a different story.
I recently found a split in the leather of the one tooled scabbard that I have. Right across the face of a smiling sun about an inch from the mouth of the scabbard.
The khukuri is the one khuk that I haven't had the heart to use, an 18" sirupati by Bura.
I also don't really know what I'd do with a sirupati. I'm more interested in "agricutural" uses than "martial" ones, so I was keeping the rig in mint condition in case I decided to sell it. I was always a bit unsure of that leather. I guess this means I'll have to keep it.
But the horn handles are just fine. Get what you like and sooner or later you'll have some of both. I like both, myself. If you just keep buying (for "research" of course
) you'll have a chance to see that both are good.
Paul