In order to decide, you might want to visit a local store and handle as many of these as you can. A lot of us will probably give recommendations, but you know best what fits your hand and which blade style suits your needs.
The Military and Starmate have several factors driving up their price. Their blade steel, CPM 440V, is almost undoubtedly the best stainless in current production knives. Their handles are made of G-10, a woven fiberglass composite, which provides exceptional strength for their weight. It also is somewhat hazardous to work and is computer-machined in a very complex fashion to inset the lock. The lock itself has seen an incredible development and testing regimen that makes it a liner-lock relied on and trusted even by most folks who don't care for that type. In short, the Military is Spyderco's flagship model and the Starmate is its soul-brother in the "collaboration" series - a lot to spend, but a heck of a lot of knife.
The other 3 knives are in ATS-55, if I remember correctly. Also a high-end steel, but a step down from the 440V. I'm assuming you are looking at the Goddard and Jess Horn Liteweights, which have molded thermoplastic (glass-filled nylon) handles. This reduces cost and works fine, but it is somewhat weaker and less "classy." No shame in that, though. The Standard is in G-10, same as above, but doesn't have the same milling so it's rather less expensive.
I personally think the Goddards are the cleanest, most efficient design Spyderco's ever produced - they feel good, look good, work well, and don't sacrifice an ounce of function doing it. The Horn offer a slimmer blade than most Spydies, nice for detail work. The Standard is, well, standard. It's a pure workin' Spydie and a fine knife.
I guess of the five I like the Military best - in fact, I think it's the best knife they make (arguably the best production folder bar none). But if I were on a tighter budget I'd pick the Goddard and be very happy with it.
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-Corduroy
"Why else would a bear want a pocket?"
Little Bear Knives
Drew Gleason:
adg@student.umass.edu
