There's 440A and 440C that is commonly used in knife blades. 440A is pretty soft stuff and doesn't hold an edge long, but is easy to sharpen and takes a razor edge.
440C is much tougher. These days, compared to super-steels like S30V, 440C is somewhat outdated and poo-poo'd by some of us snobbier folk, but it's still servicable. Benchmade is the notable exception, as their 440C is very good, the best in the business. Their heat treat is great, and it allows them to keep some of their more wallet friendly knives like the Griptillian affordable. BM is about the only company I'll buy a 440C blade from.
D2 is a significantly different beast. It's much harder, much more wear resistant, but less stain resistant. It's not quite a "stainless" steel, but it's got quite a bit more chromium than tool steels like A2 or M2.
If you want a knife that you can get messy with and not have to worry much about, get the regular 440C Griptillian. If you want a hard working one, get the Cabella's D2 one (but keep it clean and oiled when not in use). For a good, all around Griptillian, get the Ritter RSK in S30V. S30V isn't as tough as D2, but it's not as hard to sharpen, and it resists corrosion better than D2. Much better wear resistance than 440C, but easier to stain. More expensive.