Of course there is no “best exposure.” Every situation is different. But there are some best practices to consider.
These best practices assume application toward general photography. They don’t apply to people who have a creative or technical reason to do it differently. In short, if you’re NOT the kind of person who would ask this question, you may not need to read this post. (I’d write a longer disclaimer to deal with the pixel peepers and the pedants but right now I don’t have time – so take this as you wish.)
Best Exposure Practices for the Ultimate Exposure:
a. Lowest STANDARD ISO – meaning, the lowest ISO your camera will deliver without requiring you to adjust a menu or custom function to go lower
b. The smallest aperture possible, allowing for wiggle room depending on your creative depth of field
c. The fastest shutter speed possible
Now if you’re savvy, you’re realizing that to use the lowest ISO, the smallest aperture and the fastest shutter speed means that you’ll be working in some pretty strong light. And you’re correct. Remember this is a dream scenario. If all things being equal, you can do it however you’d need to do it to get the best exposure, this is the way it would shake out.
Rarely will the stars align for you like this unless you’re shooting exclusively in a controlled studio environment.
So what good is this information? Well it will help you make better decisions in the real world when you’re selecting ISO, aperture and shutter speed. You will for instance realize that in a situation where it doesn’t matter to you creatively whether or not your shutter speed is 1/500th of a second or 1/1000th of a second, and you have enough light, go with 1/1000th of a second.
I realize that the safest approach would be for me to simply ignore this question. But since it is asked so often, I wanted to try to answer it in a way that those who asked it sincerely, would benefit.
Hopefully you will dwell on the CONCEPTS here and not the specifics. If you do, you will improve both your knowledge of exposure and your ability to apply that knowledge in the field.