[barrkel]

It depends on the bike's brakes - bite point and lever adjustment - and how fast a reaction time you need.

If the brake lever can reach the throttle grip, that's generally a roadworthiness failure - old brake fluid or other wear and tear in the hydraulics. Fingers getting in the way isn't short of it. I prefer a fairly sharp bite point some way out from the throttle grip and adjust the lever accordingly.

If you are planning to brake, and you should be in a racing scenario, then four fingers gives you more control. But if I'm filtering through traffic in London, I've got two fingers on the brake and two fingers and a thumb on the throttle. I also have fingers on the clutch lever. An added bonus of keeping a couple of fingers on the brake is to help maintain throttle position to stay within the speed limit over potholes and speed bumps.