Vis-à-vis nicotine: It turns out we're all correct. In low doses, N is stimulant; in higher doses, it's sedative.
When tobacco is ignited, most of the nicotine burns away before it can enter your system, so snuff, dip, chew, etc. deliver a much higher doses proportionally--it doesn't take much snuff to get the high-dose effect. If you're snuffing regularly, you get a relaxing/pain-killing effect; if you take a little only when you need a boost, you get stimulation.
"You know what's right with this world? Nothin'!"
-Oscar, "Grouch Anthem"