Differences?
Yeah, for me, not so much differences exactly...
I eventually quit smoking cigs for the same reason as I originally quit alcohol: it was killing me.
I went for a routine dentist appointment, and he found the early beginnings of a possible cancerous white growth on my tongue, lower right side. That was in December 2004, and I quit early Jan 2005. I used nicotine patches for like 10 or 12 weeks and then nothing. I've been smoke free since. I was at my highest a 2-pack a day smoker. And real smoking, not lighting it and letting it burn out in the ashtray, and quickly lighting another... I smoked whatever I lit up and crushed it out when it was done.
Well, I certainly changed as the months went on without my returning to smoking. To stay off the smoking, of course I changed, lol... yeah, I changed...
Without the death-in-my-face action from drugs/alcohol, and ciggs, I would NEVER have EVER quit. Quitting became 'seriously important' to me only when dying as an insane drunk / loser was pretty well on the menu as the only entree being served, lol...
So I quit drugs (1978/79) while still drinking, quit alcohol (1981) while still smoking ciggs, and quit ciggs last (2005).