When you pick your nose, just make sure to dispose of the booger responsibly and the matter is over and done with. When you smoke a cigarette, the smell gets in your clothes, in all the cloth in the car, in the carpet and walls in the house, and so on. It never completely goes away, although if you give it enough time you eventually won't smell it. But I still get a faint whiff of cigarette smoke when I turn on the fan in my car, even though it's been at least 3 months since Brandi let her friends smoke in it (over my strong objections).
In short, nose-picking may be gross, but smoking is gross now and gross later. I'd take nose-picking any time.