Depends on your purpose. If you want to know if your exposures and development are good, I'd recommend minimum time for maximum black--meaning the unexposed film rebate should be black.

If your exposures are not good, though, you might not be able to tell what's on the neg with minimum time for maximum black, so you might just expose for what gives you the best image, so you can decide what is printable. When exposures vary widely on the same roll, it's not unusual for professional labs to provide two or three proof sheets exposed for different parts of the roll.