Cold turkey after 13+years. It's been about 13 years since I've quit.
The biggest obstacle for me was to not immediately light one up when stepping outside or into my garage, second obstacle was not immediately lighting up when getting into my car then while driving. Then there are friends who smoked...
After 3 days, your body realizes that it doesn't need that nicotine, the withdrawal will have already peaked (your will power is another story) your body won't demand that nicotine, your lungs begin to relax, foods start tasting tastier (especially smoked foods!), and it's really a matter of how much discipline you have. Like most others here, I'd told myself "just one for now, I can begin to quit again later" but unless you set boundaries, you're just making excuses.