For the most part, I have no brand loyalty. I will admit there are a handful of items where only a certain brand will do, but all in all I let the coupons and deals lead the way. This has actually worked out very well since I have tried all kinds of new items that I probably wouldn't have tried without the coupons. I have found some new favorite brands and in the process saved a lot of money on groceries.
Different companies at different times will put out great coupons for their products, so if you don't mind using different brands you can rack up a lot of savings by going with the company with the best coupons out at the time.
On the items that you prefer a specific brand, keep any eye out for their coupons and stock up when you see them. You can also write a letter or email to the company to let them know how much you like their product and how loyal you are. Sometimes they will send out great coupons for their products when you do this.
Sometimes even with coupons on the brand named items, the store brand is a better deal. In this case, I'm going with the store brand. The goal isn't to use as many coupons as you can but to get your groceries at the lowest price possible. Whatever the best bottom line is, go with that!