My personal preference would be for something in the 14" to 16" range with a weight of around 22 to 26 ounces.
A second vote for this, although my preference is 15"-16.5" and my ideal weight is 24-26 ounces. I suspect Ilbruche and I are after the same thing here -- small enough to be convenient, but just large enough to chop efficiently.
You'll find that there's a certain minimum size requirement for efficient chopping. Something smaller will work, sure, but you're going to expend more energy making up for the amount of work that the tool is no longer doing for you. My cutoff is 15" for this although obviously, there's a bit of wiggle room here. Likewise, after a certain length the chape starts stabs you in the calf if you take a knee, the scabbard hangs up in tight spaces, and the length strains the wrist. Too little weight and it won't cut, but too much weight and it tires you out unduly. ~15"/25 oz. or in that ballpark is a figure that comes up a lot as a good one.
As for models, certain things recommend themselves. One school of thought is that the tool ought to be optimized for chopping, particularly if it's going to be this small. The Ang Khola and Ganga Ram are often mentioned for this. Both styles work extremely well when of this size. (They work in other sizes as well, but I believe that they're at their best here.)
Tang design is a matter of personal preference. I haven't noticed a full tang transmitting significantly more shock than a hidden one, and I've never experienced any tang failure at all. A full tang ought to be a bit heavier and more neutrally balanced than a hidden tang but consider the overall picture, not the design method. If it works reliably I'm not particularly concerned about how it was constructed, only that it works.
Larger khukuris can tackle larger tasks obviously, but when I have to pack the thing there this is what I want.