Rigel, I've got to give it to you - that was classic!
To answer your question, Premium for me - I have a Supercharged engine, and I actually do feel quite a difference in between the regular and Premium... I just used the regular a couple of times, and didn't like it at all - less power and mileage...
On my old car, with a regular engine, I didn't feel any difference, so I used regular.