I agree, you should always use both brakes. Just vary how much force you are applying. I use more back brake on the mild brake situations, and the more I need to stop the harder I push on the front brake compared to the back. On dry pavement front-only will be the fastest stop, but on wet pavement your front will start skidding earlier and so you want some back brake as well. In an emergency you don't necessarily have time to think wet-or-not, just hit both brakes and adjust.