I have 2 Kit Carson's left in my collection... a 3.5" Model 4 in ironwood and D2, and a 4" Model 4 in ironwood and 420V (S90V now). Several others have passed through my hands, including one in Stellite 6. They are/were very finely executed folders. They will appreciate more rapidly than a Terzuola due to Kit's health. My only quibble with the Model 4 is the lack of a "guard" aspect of the handle design.
I have literally lost count of the Terzuola's in my collection (north of 10, south of 30). So I have a bias ;-) ... partly because Terzuola's are relatively more available in a variety of materials and at prices south of nosebleed. The ATCF is one of the earliest tactical liner lock designs, and is STILL one of the finest all around folder designs extant. It still looks and feels current. The handle design gives the index finger a sort of "Guard", and the blade shapes range from the earlier spear points to a modified spear with a different grind of late... to the addition of a fuller or blood groove, also of late.
I have one ATCF one that has carbon fiber scales, no bolster, and it's ~ 2.5oz... a perfect folder for e.g. backpacking. Super light for a 4" blade of such build quality. I have various bolstered ATCF's, love them, but they get heavier with bolsters and especially with fossil mammoth scales. The Eagle Rock design is also excellent, but gets heavy too... I have a couple that go 8 oz, which is too heavy for daily carry, especially without a pocket clip (for me, carried in a slip pouch/sheeth like CRK delivers w/ a Sebbie, 8oz is too heavy feeling in the bottom of a pocket). The heavier they are, the more they need a clip for pocket carry.
The ATCF (proper) has a 3-7/8" to 4" blade. If you want a Terzuola spear point with a 3" to 3.5" blade, it's his TTF-6. He makes a bunch of blade shapes in the TTF series, all 3" to 3.5". Wharnies, modified wharnies, drop points, spear points.
Both makers are top of the top.
If you plan to carry and use, I'd do a Terzuola. If it's for investment purposes and will be a safe queen, a Kit Carson.