What's Best to Whiten Very Brown Stains in Between Teeth Due to Smoking?

Without a doubt, the best way to eliminate brown stains in between teeth from smoking is TO STOP SMOKING.  When smoking is not an issue, there are many ways to remove these stains.  Thorough brushing with a high quality toothpaste can remove most stains.  A professional cleaning will remove what you miss.

Whitening is not the best solution.  It will have an effect, but these whitening products are best suited to lighten overall tooth color.  They do in part remove stains, but that is not die true function.  Best to quit the habit, you may find the brown in between the teeth disappears

Cosmetic dentistry can whiten even the discoloration from smoking. Trying whitening toothpastes or whitening gels is just a waste of time and money at this point. The most effective way is to start with a great dental cleaning. Some tobacco stain just needs to be removed by hand by the hygienist. 

Some very brown stains between teeth are actually cavities. You will need a good examination to see if that's a problem for you.

Some very brown stains are actually older white or composite fillings. They can absorb a lot of stain either from the porousness of the old material itself, or from the edges of the old fillings losing the seal, and re-opening allowing a second cavity to start under the first one.

If none of these other issues are problems for you THEN it's time to consider teeth whitening. Success from teeth whitening comes largely from matching one of the whitening techniques to your whitening personality. Different people need different ways to whiten their teeth-no one way works for everyone.