I've had nothing but issues with Shell gas. Seems to be good on the east coast and a toss up on the west coast.
I use chevron pretty much exclusively, but will use 76 if they are not close by.
Shell I avoid at all costs. This is because it put my supercharged 330 in limp mode, as well as a friends M3, and a friends 335, almost immediately after fill up. With Chevron, no issue. On the east coast Sunoco and BP would be my choices - 94 octane of course
This is just my experience.