Do you use the handbrake or footbrake when driving a automatic car when waiting at traffic lights?

Always use the handbrake. If you are hit up the back your foot will automatically come off the brake. Jumping you into the junction.

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Foot brake for the most part, at railroad tracks I just put it in Park.

I use the handbrake and speed up the engine before it's time to take off.

According to the UK highway code, rule 114, "You MUST NOT use any lights in a way which would dazzle or cause discomfort to other road users, including pedestrians, cyclists".

That includes keeping your brake lights on, by keeping your foot on the brake pedal, when waiting at traffic lights if there is another car stopped behind you. The safest approach, whether in an automatic or a manual, is to apply the handbrake as soon as you stop, but keep your foot on the brake pedal too keep your brake lights illuminated until the car behind has come to a stop, then release the brake pedal to extinguish the brake lights.

Anyone using the hand brake shouldn't be driving!

The HANDBRAKE is for parking. Use the footbrake for driving.

Use the foot brake while you're in traffic, that's what it's there for. When you take your foot off the brake, the brake lights go dark and traffic approaching from behind can't tell if you're stopped.

You also do not harm or wear out the transmission by leaving it in Drive, the torque converter is designed to allow slippage at engine idle.

The idea is that if you have time to use the handbrake you do so. It is, though, useful to keep your foot on the pedal until you know the driver behind has seen the lights and realised you've stopped.

Use the handbrake.

Be kind to the driver behind, it stops the glare from the brake lights at night