The answer to that is right here:
http://www.bladeforums.com/forums/showthread.php/601448-First-Khukuri-Recommendations-and-Reasons
Ang Khola (AK)- Our #1 best-seller, The H.I. Ang Khola is a beast of a chopper. Ang Khola means back-valley or "back-hollow", referring to the forged depression on the posterior blade spine that provides for forward weight distribution and fearsome chopping ability. This knife is considered by many experts to be the toughest knife in the world, it has chopped up steel drums and junk cars with no damage to the knife. In lateral strength tests that destroyed other knives, the Ang Khola would not budge. The H.I. Ang Khola has been recommended in articles in every major knife magazine in the US. While the larger versions (up to 20) are used primarily in heavy chopping tasks, the 15 model strikes a good balance between portability and chopping prowess. Chiruwa style Ang Kholas are also available for those interested. The Chiruwa Ang Kholas are the only khukuri warranted for use as a prybar.
British Army Service (BAS)-Our #2 best-seller, A jack-of-all-trades in a packable length, this khukuri is very easy to throw on a belt or lash to a pack. It chops well, splits well and will do most camp chores with relative ease. Although lighter than khukuri of the same size, it doesnt sacrifice much in chopping power for weight manageablity during extended trekking. This is the same size and style khukuri (but considerably better quality) that is carried by present day Gurkhas serving in the British Army. Battle tested and proven.
World War II (WWII) -Our #3 best-seller, Uncle Bill favored the WWII model as an all-round khukuri and rightly so. The workhorse of the Gurkhas during WWII, this model saw service in both Europe and Pacific theaters. This is probably the best combination of weapon and tool in a khukuri that can be had and is favored by many Bando practitioners. The WWII will chop, split wood, balance, and maneuver well. Its relatively longer handle also facilitates different grips. This model hits above its weight class, is faster, and is less tiring than other heavier models.The WWII is also easily packable for trekking and camping.