I always have very good luck using a small diameter drill bit as it is very fast and doesn't make much of a mess. 5/32" is my preferred bit size, but anything around that should work. Avoid anything larger than 3/16" or you'll just be drilling out a bunch of the lock barrel for no good reason.
Be sure to use a nice sharp drill bit, dull bits are not good for this task. Also, since you're cutting metal, you'll want to put some kind of lubricant on the cutting tool. If you have cutting oil put that on the drill bit, otherwise just put some 3-in-1 oil on it.
Run the drill bit right into the center of the lock and go straight back. 99% of the time, the tip of the drill bit will zip down the nearly empty middle of the lock barrel in about 1 second, where it will hit the mounting screw for the lock tab and unscrew it instantly. This will cause the lock tab to fall off the back side of the lock, and you'll be done.
If you have one of the 1% unlucky locks that won't drill out this way, then you will need to start running larger and larger bits down the center of the lock until you get it.
When I'm drilling a lock at a customer's house, I always throw a shop towel on the floor below where I'm drilling to catch metal shavings and oil.