I've always favored Rembrandt because I thought it left my teeth feeling clean and healthy. It wasn't until I went abroad that I noticed the full effects of Rembrandt.
A few years ago, I spent about three months in Europe, and about a month in, my tube of Rembrandt ran out. Not thinking much of it (and because I didn't want to go through the hassle of finding good toothpaste), I started using generic brand toothpaste. After a few weeks of using the generic toothpaste, I started noticing that my teeth looked yellower. Upon closer inspection, I saw brown stains on my upper and lower center teeth! Granted, I did drink more red wine, but the amount of "staining" foods I consumed (coffee, tea, etc.) did not change... In fact, I didn't drink as much coffee or tea during those months as I do back in the states.
When I got back home, I had to use whitening strips to get my teeth back to the previous white color, and I immediately started using the Intense Stain toothpaste to clean out the stains (previously, I just used the green-boxed Deeply white toothpaste from Rembrandt). Eventually, my teeth retained their original white hue, but I was shocked that a switching toothpaste could have caused such a noticable change.
I realize that there must be other factors, i.e., my foreign toothpaste could have been exceptionally low quality as it was provided for me at no cost. But still, I've not used any toothpaste other than Rembrandt for years, and no matter how much coffee/tea I drink, I'm still getting compliments on my teeth.