Robust covers a lot.
CAK - You're going to be able to chop anything with it. Dedicated tool. Heavy. You'll tire out quicker.
M-43 - Still going to chop...pretty much anything. The edge profile and blade shape make up for the lesser weight. Straddles the line between multi-tool and weapon well, leans a bit towards the weapon side. Still thick enough to stand up to anything you throw at it. WildMike used his while building a couple log cabins.
The M-43, with its curved spine....well, mine feels like an extension of my arm. The balance and the flow is just right, easy to aim, etc. But when I'm using the CAK, it's like swinging an axe. For me, it's a little ungainly, and thus don't use it as much.
If you're between the CAK and M43, pick the M43. (Keep the BAS in mind though. It's a wonderful little jack of all trades knife. M43 just beats it because of size and weight, means it has better chopping performance. BAS could do cleanup jobs round the yard just fine.)
Now...if you're looking for something that goes through vines and thin wood easier, you've got a whole different set of models to look at. Sirupati, Gelbu Special, Chainpuri, Chitlangi, etc. The thicker blades just kind of push it out of the way without cutting.
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