I don't try to stick to one at all. With the fluctuations in prices around the country and even in the different cities, I'd go nuts trying to stick to one.
It depends on what I want to cook that week, what we're hungry for or how labor intensive we want our food to be. In Florida I was used to having fruits and veg whenever I wanted. Here in Texas you have to pay for what you want. And a lot of things come from Mexico here instead of the warmer US states.
But one drawback in Florida was tourist season/vacation season made prices rise. So did Snowbird season when all the Northerners came down to get warm. Up the prices went.