Well, many addictions have withdrawal effects that are serious or even life threatening. Nicotine withdrawal effects are mild discomforts that go away after a few days.

I've known people who quit heroin and struggled to quit cigs. Which one is "harder" to quit is probably subjective and depends on the person, but there is a lot more going on than physical withdrawal symptoms.

I commented earlier in this thread, but I think one of the toughest aspects of quitting smoking is breaking the ritual.

I had so many friends who smoked, and our independent desires to quit were definitely not in sync. I don't doubt that this was one of the major factors in me drawing out my quitting process.

I quit smoking. I'm pretty sure you have never done it.