I can't compare cannabis and caffeine because I don't enjoy cannabis so have never become chronic with it; but caffeine is seriously insanely hard to quit. 3-4 days isn't it for me. The one time I kicked it for a chunk of time, it took about 3 weeks before I felt normal enough to feel I'd really kicked it, and lost the craving. I'm very sensitive to the stuff, and I love (good quality) coffee. After a couple months without it, I just ended up back drinking it again.

In comparison, I've smoked cigarettes, cigars, pipe tobacco, and never had a problem quitting. Few days of craving after smoking for a few days, then kicked it. Coffee... brutal brutal brutal