Kanthal (iron-chromium-aluminum, "FeCrAl") already has a long history of use in heating elements. It can withstand high temperatures and forms a protective oxide layer on the surface that is thermally conductive and electircally non-conductive.
Nichrome (nickel-chromium, "Ni80"/others) is similar to Kanthal, but offers lower resistance with the same coil size. This allows for higher power output on a mechanical/un-regulated, and faster ramp-up time on a regulated device, when compared with Kanthal.
Stainless Steel (iron-chromium-nickel-molybdenum, "SS316L"/others) has even less resistance still and, unlike the other two, can also be used in the appropriate temperature-control mode since the resistance value increases predictably as it heats up.
Nickel (pure, "Ni200") was the first wire used for temperature-control and, unlike SS, can only be used that way. Nickel wire if used in straight "wattage" mode (no temp. control) can get hot enough to emit harmful substances, which occurs at much lower temperatures than the previous examples.
Titanium (pure, "Ti") is like nickel, in that it has very low resistance, and should only be used in the appropriate temp. control mode, never in wattage mode (or bypass/direct-output/anything other than "TC-Ti" for Titanium or "TC-Ni" for nickel).
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Some people report a "metallic" taste with either Kanthal, Nichrome, or SS coils, and swear by one of the others as having a "cleaner" taste. Then again, others will say the exact same thing, but in reverse. I'm not what you'd call a "super-taster," and personally I don't notice a difference in taste between the metals. I use Kanthal, because that's what I started with and still have some left, and also SS because of its versatility and ability to be used in temp. control and wattage/bypass modes, and even on completely unregulated, mechanical devices if I wish.
