I use premium (or whatever octane specified in my owner's manual) from whatever Nationally recognized gas station is nearby when I need gas. Shell, Chevron, Mobil, Texaco, etc. all will do for me. I've never noticed any difference in performance in any of my cars among any of those gas stations.
I think using different gasoline every now and then is better, actually, because I think they all use slightly different detergents, which are each slightly better at cleaning differnt types of deposits. Just a feeling, I have no proof of that.
The reality is this is not an issue that I give any thought to. I just use gas from any of the many reputable companies.