I still think there is luck, it depends on where you live and where you shop in the UK, VT. My perhaps as a smoker can not always taste the differences but there are some things like a sack of main crop spuds or onions I'd use Groveland, a local farm shop in preference to a supermarket and they are reasonably priced.

OTOH, while it doesn't answer your GM question, some things simply can not be beaten from home. Peas, runner beans, salad potatoes, spinach, asparagus, sweet corn, salad leaves, tomatoes.... If I do have an opinion, it's a freshness and growing for flavour rather than a growing for qty.