Best store-bought brownies?

It's better if you bake it yourself.

Bake them...there is no such thing as a good store bought brownie

Oh, wow.
 
Ask for the recipe.

Nothing beats self-made brownies. Nothing.

What all of these guys said. It tastes better if you make them yourself.

Costco, I guess, to answer your question.  But, yes, homemade brownies are superior.

True, they taste better when you take them freshly out of the oven, but for ones you can buy in the store.....
 
Subway and 7-11 have some really good already-made brownies.  As for the mix, I would personally choose the Hershey's pre-made mix that you can typically find at Costco. 

I guess I shall make them myself.

If you are lazy, try some microwave brownies.  They're okay if hot, but they get a bit crummy if they stay around for too long.  Nothing beats fresh, but sometimes you just don't care enough to make the treat from scratch.

" Nothing beats self-made brownies. Nothing. "