I've thought about this topic before and have read various opinions. Since I now own more than a dozen HI products (believe me, it doesn't take long to build a collection and you'll have a ton of fun and make many friends here in doing so), here is what I can share from personal experience and the products I own and I'm sure others will chime in:
Note: my Khuks tend to fall into the 15-in to 20-in category and I'll mostly comment on HI products from the perspective of handling, speed, and balance, which are of key importance when using a knife for self-defense (you should of course train in distance control, take down defense, ground combat, keeping the weapon "alive," among other things; but most importantly respect the fact that a knife's point and edge can cause devastating effects both intentionally and not even in the hands of an untrained person who may come at you from odd angles).
My favorite candidates:
1. 15" Katunje - by far the best balanced Khuk I have and feels like a natural extension of my arm. It's also Auntie Yangdu's signature knife. This Khuk feels so good in my hand that it's almost second nature to wield. It's also feels balanced without any sacrifice to power and can chop as well as a similar-sized AK.
2. 16" Sirupati - Handles very well and has a thick spine but the difference between the Siru and the Katunje is that the Siru feel more like a chopper in my hand (more forward weight distribution) than the Katunje. I would never have guess it at first and it still doesn't make much sense but actual practice tells me it's true. Maybe my Siru has a thicker spine than usual? But in any case, the Siru still feels faster than all the rest of the bunch.
3. 18.5" Chilangi - Slower than the Siru but not by far. If the Chilangi were 16" instead of 18.5", I think it'd be faster. But the knife is beautifully done with fullers and still very maneuverable for a big boy. The weight distribution is actually less forward feeling than the Siru but due to its length, it's slower.
4. 15" AK - I have a silver mounted carved AK by Master Kami Bura and its balance is awesome for a chopper. AKs are generally not known for their speed but the 15" version still feels reasonably fast. I would definitely place the 15" AK behind the Katunje, the Siru, and the Chilangi, however.
I would not recommend any other Khuks that I have for self-defense because they feel like choppers and tools (WWII, Boomerang, Hanshee, bigger AKs, UBE, YCS, and all the favorites). But there are definitely many other choices for you e.g. Kobras (very fast). As for non-khuks, however, my HI Classic Bowie (I bought it because I love horn handles and it has a big piece of carved horn) feels like another extension of my arm. It was made by Kami Sher the Younger and features a thick blade, chiruwa handle, thick steel guard, and a razor sharp edge. It handles like my Katunje from above and my Spyderco Rock Salt (a non-HI product reference), which speaks volumes about its maneuverability. My short Bura Bowie would come next (more forward, chopper-like feel). And if you want a pretty utility knife that can also be used for self-defense (think big sharp butter knife with a carved wood handle), I'd recommend a Kumar Karda.
