Welcome
Well since you are planning on using this as an all around bushwhacker/shelter builder/etc...then I might suggest you forget about the kobra. It's one of my favorite blades, but it's more of a fighter and the weakest of the slim khuks. Still plenty strong, IMHO as the 20" versions come in with a blade thickness of about 5/16". That's the same thickness as a Cold Steel Trailmaster. The Siru, Chain, and Chit are all very close and it's really going to depend on the mood of the kami the day he made the blade to pick any of them over the others. They are all very close with the siru leaning more towards a chopper than a fighter.
Now.....let me add just a little more fuel to the fire. Have you thought about the Sher Attitude Special? They are not found on the site, but they do come in during the deals of the day quite a bit.
Here's a pic that our very own Mike (Ad Astra) took of his some time ago:
The SAS is the blade in the middle. As you can see, it's not EXACTLY a khuk as it has no cho. However, this might just be the end all to your needs. Generally, they come in at 18" in length over all, weigh 20-23 oz, come with no chakma or karda so they pack very flat. The curve of the knife causes it to hook material as you chop so it does very well for its size on wood AND grass/leaves. The only product that I have that does a better job of light grass and vines is the hasiya which is basically a hand sickle. The SAS is going to be much stronger than say a kobra, but very friendly to tote around. Another feature that may or may not matter to you is that because it has no cho, you can choke up on the blade in that empty space to do finer work. Also, chos tend to look "alien" to those not used to knuks....so they automaticly think "weapon"

The SAS is alllllll business
Good luck! The nice thing about HI is that ANYTHING you get will work and not let you down. Just try one that works for you. I'm sure you'll be picking up more
Once again, welcome!
Jake