I'd agree that if you're primarily going to be cutting vines and light branches, you'll do better with a longer, thinner khukuri. If you want to chop down trees and split small logs, I'd go for one of the shorter, wider, thicker khukuris.
Since you want to be able to chop "anything you come across," I think you said, you probably want to rule out the VERY thinnest khukuris, such as the kobra and chainpuri and maybe chitlangi. The natural choices for you, I think, are probably the sirupati and the "Gelbu special", sometimes known as the "Udhaipur" variety. Either the sirupati or the Gelbu special will chop most wood just fine, and they tend to be long and thin enough to get the kind of tip velocity you'll want for vines, thorn-bushes, etc. I'd go for a sirupati or Gelbu special somewhere in the 17-inch-or-above overall length range. (You won't be unhappy, I think, given your preferred appliation, with a khukuri with an overall length even up into 20 or more inches. If you're used to a machete, a khukuri isn't going to seem too long, and the physics of swinging a knife dictate that it's easier to get a longer blade going quickly at the tip than a shorter one.)
For vines, etc., the heavy choppers--ang kholas, WWII models, Ganga Ram models--will probably be too heavy. You'll find them tiring your hand, and it'll be tough to get the kind of tip speed that really zips through light, springy foliage well with them. The heavy choppers eat right through seasoned hardwood just fine, in my experience, but they'd do less well as substitute machetes.
The British Army Service model (overall length 15 inches) is one of my own favorites for practical use--it's a bit short and wide (chopping-oriented) for clearing vines as a substitute machete, but it's also somewhat light and more manageable than the 18-inchers. Thus, for your stated applications, I'd stick with the sirupati or the Gelbu special, and avoid one of my usual recommendations, the BAS. Sirupatis tend to show up for sale more frequently than Gelbu specials, so my prediction is that that's what you'll end up with.
I hope that helps.
