I get asked all of the time about options for bleaching teeth. The two most important criteria for bleaching are the concentration of the hydrogen peroxide and length of contact time with the tooth. Right off the bat, over the counter products are at a severe disadvantage because they do not have as high a concentration of hydrogen peroxide as what you can get from your dentist.
The only store product my patients have had success with is Crest White Strips. I do not have any financial interest in P&G, but white strips do seem to work. The downside is that they are not inexpensive and I am hearing that many people need to use more than one kit to get the results they want.
By comparison, bleach trays made in the dental office are more expensive up front, but in the long run may be a better choice. This is because the concentration of bleach is higher when using bleach trays. After bleaching, teeth will start to darken again. A few years down the road, when you would like to refresh your color, you can reuse your bleach trays with bleach from the dental office. This is usually less expensive than buying more White Strips, and it does a better job.