Always two fingers on the brake lever. I've had numerous situations on the highway as well as on larger streets, where someone would suddenly pull in front of me, and instead of a panic braking situation if I had my fingers off, and had to spend precious milliseconds and feet traveled, reaching for that lever, it was more of a "meh" situation where an instant gentle squeeze would slow me down enough to avoid the car, and then quickly pass them.
Front brakes are not an ON/OFF switch as most of these scary stories of going over the bars or locking the front, would suggest.
P.S. Ergonomics of it just need time to get used to. There is absolutely no strain or discomfort, as well as no loss of throttle fidelity in my palm and wrist, from having two fingers resting on the brake lever. Having them there, doesn't mean I'm tense and ready to pull the trigger. I'm just not wasting time by reaching for the lever, ESPECIALLY in a panic situation where every foot counts. Comparing this to having a left foot on the brake pedal in a car, is pretty stupid imo.